
That camera has quite a few fans here. Gresch, KewlX5, SANguru, B-Line, and I all have the 40D. I'm sure there are others but those are the peeps I know for sure have it.
I just got mine about a month ago. I love it. I started out looking at a Rebel XTi for its very attractive price point but after handling them both, it was hands down in favor of the 40D. I considered the 30D but looked at the purchase as a longer term investment and plan on keeping the 40D as long as it still works. It would likely become a backup/second camera. It was better to spend more and that was the majority opinion of those I asked.
The 40D was more than twice the price of the XTi and worth it. I just saw but did not handle, the XSi today. It looks bigger than the XTi which is a good thing. The price is about $900 with a 18-55mm lens. That might be a good alternative since you're looking to get is as a gift from someone. $1350 is pretty steep unless you have some generous benefactors.

The 30D is also very nice but from what I've read, the extra pixels are not as big a deal as some of the other upgrades, like Live View, Digic III sensor, 3" LCD, and other improvements.
Whichever you get, you'll be spoiled. I was using my 40D all weekend a couple of weekend ago, shooting about 900 pictures, and I used a Canon IS850 (something like that) to take pictures of its owner and while it is an excellent P&S camera, it felt so slow compared to the 40D.
I hope you get it for your b-day.