You be the judge, is the Canon 30D worth the extra few hundred dollars over the Canon 20D? Digital Photography Review (http://www.dpreview.com/) has the most complete review of the Canon 30D I've seen. In fact, it's probably the most complete photography review site you can find anywhere on the web.
Although the 30D has many technical advantages, the feature that stands out is the 2.5 inch LCD. This is a huge improvement over the 20D and the one feature which may be worth the extra money on it's own. I tried one at my local Best Buy (http://www.bestbuy.com/) store and really liked it.