I also use a 20d and love it.... He currently has a 20D and is one of the many serious hobbiests waiting for Canon to release a full frame digital at the right price point for a non-professional. He has read tons of reviews and looked at the new 50D and he says he'll settle for one of those if his 20D gives out.
Our money is in the lenses, not the camera body anyway. Those will be portable to the next Canon camera body. ...
Here's a bit of warning, however. The 20d and it's 1.6x conversion factor brethren (30d, 40d, 50d & Rebels) can use both EF and EF-S lenses. The full-frame canons can only use EF lenses. Therefore, if you upgrade to a full-frame camera, you will have to replace any EF-S lenses that you own.
In our case, this won't be a problem. This has been dh's excuse to only buy "L" series glass for the past few years. He went with the 20d instead of the 5D because of it's speed for swimming and dance shots. Like I said "all of our money is in the lenses".