30D vs. 20D? Are the differences worth another purchase?

My first canon dslr was the original Rebel also known as the 300D, for its time and considering what that camera cost, it was competent but it can't hold a candle to a 20D and even less so to a 30D. I shoot a lot of karate for my school, the 300D Rebel only has 3 fps which just isn't enough for board breaks and other karate antics. I was ecstatic when I bought my 20D because I finally had a camera that could handle what I needed it to do. The 20D is a very competent camera but when shooting in mixed lighting environments (such as mercury vapor gym lighting with flash) it has serious issues with white balance which I've somewhat found solutions for, however, the 30D has vastly improved white balance handling in my opinion and at least for me that was a tremendous upgrade.

The 30D doesn't seem to offer a great deal of improvement over the 20D at least on the outside. The obvious upgrades are larger LCD panel on the back, photo styles and spot metering mode, less obvious upgrades are no more one hundred image folder limits anymore, 3 or 5 fps continuous mode and a supposedly upgraded shutter system that should last a bit longer.

Externally there really isn't much that tells you that this is a different camera from the 20D, control layouts are the same, lcd panel still present on the top right of the camera instead of the back like the rebel and it uses the same battery grip as the 20D, the bg-e2. The 30D has the same C sized sensor as the 20D and both are 8 megapixels. If you turn the camera around the lcd panel is obviously larger than that of the 20D (and I think it's a good bit sharper too, this does make a difference if you're trying to determine if your image is sharp without printing it or loading it on a laptop).

What's in the box:
No differences from the 20D, you get the body, warranty card, book, bp-511 battery, battery charger (but they switched from one with a plug in ac cable to one that just plugs in the wall)

Setup:
Not really any setup, you charge a battery turn on the camera set the clock make your settings. I believe there is a button cell in here someplace backing up the clock and internal settings (I believe it was in the battery compartment on the 20D I'm sure its in the same spot I just haven't tried to spot it yet). If you desire to use iso 3200 mode it must be activated in the menu (but the way it's activated on the 30D is a bit easier than it is on the 20D).

What else do I need to use this camera?
Battery Grip/more batteries:If you use IS lenses such as the excellent 28-135 IS or the 17-85 IS then you want the battery grip because the IS system sucks juice just like anything else. Two batteries will get you through a long shoot. You can buy these batteries reasonably on ebay, just be certain you purchase only the 7.4V versions, of all the batteries like this that I've seen fail it's the 7.2 units that die first. The BG-E2 battery grip from canon runs over a hundred fifty dollars, there are several third party products that perform the same function available on ebay in the 70 dollar range, they're fine I bought one for my 30D and it has been great. The canon unit has a door on the back that opens and the batteries seat front to back, the third party unit I have has a carrier that slides out the right side and the batteries are loaded end to end. The canon unit will not accept anything but the original curved top bp-511, the third party unit I just bought will probably easily handle the flat topped 511 batteries that you also see on ebay (haven't tried yet but since they aren't so tightly seated as in the canon grip they should work). Either battery grip will use AA's in an emergency.
Flash: The built in flash is not good except for the occasional snapshot, you want either a 550ex, a 580EX or a 580EXII or the metz AF-58 1C, of the three the 550 will be cheapest since it's not made anymore but the 580 and the metz are a bit more powerful. I have the metz unit but since its a brand new product I can't yet get the external power cord for it so until I can test it shooting my chosen sport I can only say it's a good external flash that supports the camera as well as the canon unit.
Several fast medium sized compact flash cards:
I have used Lexar, Sandisk, and Ridata compact flash cards in my 20D, so far they also work in the 30D. Remember, this card has high speed buffers and is capable of respectable memory transfer to the card, don't buy less than a 150X card for this camera. The combination of the fast buffers and a fast CF card means your buffers will never get so full the camera stops (like happened a lot on my 300D). Don't put cheap tires on your firari, give your baby good memory cards.

My experiences with this camera and differences over the 20D:

I've had this about a month, I lucked into a floor model marked down ridiculously low at a local circuit city. Outdoors I feel this camera tends to underexpose the subject a bit, however, indoors.....I think canon's gone a long way to improve flash exposure logic with this camera. On the 20D I usually felt flash exposures were bit dark and there are big discussions on the camera forums about how those shooting people feel that their subjects often get underexposed if you don't exposure lock onto skin before shooting your pictures.

I finally got a chance to shoot a karate test last Thursday. I did my usual procedure of setting a custom white balance using a expodisc filter (www.expodisc.com) on the end of my chosen lens and a green omnibounce on my flash (in this way flash light is closer to the same color as the mercury vapor lamps in the ceiling). I used the "faithful" style setting and the new spot metering mode and I'm extremely happy with the white balance, exposure, and color saturation of my pictures. Before I had awful problems with heavy yellow backgrounds on my pictures with the 20D and while the expodisc was able to correct some of that, the pictures are FAR superior on the 30D, I believe canon's made some improvements on their white balance logic. This camera is equally responsive in high speed 5 fps mode to the 20D.

So far I really believe the improvements made on the 30D make it worth purchasing the new body. At this moment, with the 40D due out soon the price difference of 20D vs. 30D is pretty negligible. You can still find both the 20D and the 30D for sale online and on ebay, get the 30D if you want my opinion you won't be sorry.

Selling points for this camera:
Digic II sensor (widely considered the best sensor)
capable of shooting competently in ISO 3200 mode (but you probably want a product like noise ninja to process out some of the noise)
Large LCD panel
Canon offers IS (image stabilization) on some lenses, Sigma is now also offering this on some third party lenses made for this camera
30D has a true spot metering mode (20D didn't really have this)
Large buffers, 5 fps, RAW mode for the photo conosseur

Bad points?
Canon glass a bit pricey
If you buy third party lenses sometimes firmware upgrades will make them non-functional (but lenses can be rechipped a few times)

update: Still love my 30D and I truly do think the white balance logic is tons better than the 20D. Be careful of third party grips. My Targus grip after only a couple of months started being quirky (buttons stopped working, even loss of power issues). I think the battery door just got a little loose and the batteries start losing connection but it sure didn't last very long, perhaps it is worth spending the extra on a real canon grip. They took it back under warranty but I still don't have a replacement. Some things like hoods etc. are worth it to save the money on third party products, items like the grip may not be such a bargain.

update: Every time I use this camera in a difficult lighting situation I'm very impressed with the improvements over the 20D.....the white balance logic is really that much better. Bought a Sigma EX 10-20 MM, love it and it's cheaper than the canon product by several hundred bucks. Now that I've got my first third party lens I do notice a couple issues (like not properly focusing occasionally--but not often) but in all it's as sharp as my canon glass and just as fast focusing. If buying sigma go for only EX or EX DG line because those have the good motors that are as fast as the canon focusing motors. I also bought a Metz AF-58 1C flash unit with a p76 power package, this setup is as powerful as the canon 580 flash and with the power package it very competently keeps up with the camera even shooting full out 5 fps (in iso 800+). The 40D is now out and can be found for sale at about the same price point that the 20D and 30D were at. The 40D offers 10 megapixel sensor, however, I've seen a few opinions saying the lower quality sensor on the 30D may actually be superior in some ways. The extra megapixels will be nice if you're cropping otherwise I can't justify that kind of purchase right now.