I bought the 20D just as the 30D was announced...then I had a 30D in my hands and, yes, the back screen is a good upgrade. But I didn't have the chance to play around with anything else. There is supposed to be a longer life on the shutter mechanism than on the 20D but considering the amount of usage I figure I'll have on the 20D the difference in price (20D markdown vs. 30D initial price) was enough to make me go for the 20D. Did I make a bad choice? Well, as the 20D has proven itself to be a very good stable camera I'm okay with this choice.
One thing of note is that the roll out cost of the 30D is actually less than the 20D's roll out was back 18+months ago. So I figure that in a year's time the 30D's price should be inviting to pick one up at that time.
As it is had you been in this situation of going into digital for the first time the 30D was all but vaporware...mere rumours...so you would not have had the choice.
Gkulka has it right...lenses make the image. So your choice is to save a bit of cash going with the 20D and use that extra money for some good glass...or pay the higher price for the 30D with it's (realistically) minimal upgrades.
Make your choice and get out there and shoot...no regrets, just images.
"Beauty is more than skin deep"