I completely disagree with you, Village Idiot. I own an XSi (450D) and a 40D right now (from my dad when he bought the 50D) and I use the XSi almost exclusively.
Using my dad's 50D I feel I can comment on this discussion with a good amount of knowledge and experience backing me up (I also asked my dad who's been an avid photography buff for upwards of 35 years his thoughts on it, as well) as the T1i is *very* similar to the XSi in most regards.
Here are the strong points of the T1i: Smaller, weighs much less (less than 2/3 of the 50D), comparable picture quality because of the identical sensor in the 50D, for general purposes (with very few exceptions) nearly the same options. 720p/1080p video capture that looks *fantastic*.
50D: Faster burst rate (These are only IIRC, but 3.6fps on the t1i and 6.4fps on the 50D), faster shutter speed (1/8000 as opposed to the 1/4000 in T1i), much heavier and bulkier body (some people like that), better viewfinder and AF points that acquire focus slightly faster. Also provides a higher ISO rating (but even with Strong noise reduction on you'll see somewhat heavy noise at the maximum iso setting).
Here are our results: I'm 25 years old and very active (sports, Air Force, etc...) and I couldn't be happier with my XSi (even though I also have a 40D which is very similar to the 50D). My dad is a 60 year-old who, although active, uses his camera for mostly events (weddings, parties where he's not constantly taking pictures, etc...). He prefers his over the Rebel series by far (he had the original digital rebel before buying the 40D, then the 50D) while I could never be persuaded to use the "pro-sumer" line of 40D/50D for long periods of time.
The question is what you'll be using it for. I don't normally take pictures of F1 races or anything but when I have the 1/4000 shutter speed was *completely* sufficient (and the only lens I even use it on is my 50mm f/1.8) to stop the cars dead in their tracks (used it at an airshow and it looks like the plane was just hovering). 3.6fps is almost always sufficient except in very rare cases (at airshows I would like to have a higher speed -- my dad was with me with his 50D -- but I still don't bring my 40D because of the other things I don't like about it). The viewfinder on the 50D is definitely very nice, but truthfully I also like the *controls* on the Rebel line much better.
The 40D/50D has a beautiful LCD on top of the body that displays all relevant information, but on the Rebel line all of that information is displayed on the LCD on the back of the camera anyway...and if you're going to take your eye away from the viewfinder I'd rather just pull my head straight back than have to either pick my head up higher or lower the camera to see the info on the top screen. Of course, all EOS cameras keep the information in the viewfinder as long as you have some type of lock in place.
My advice would be to go to a camera store near you, play around with both cameras for a good 10-15 minutes a piece, and make your decision. Although my dad loves the pro-sumer line (and would never buy another consumer-series) he also agreed with me that you should probably go with the T1i. Going with a high-priced body is completely useless at this point in your photography journey. I know *PLENTY* of professional photographers that still own and occasionally use a Rebel-series camera (because of it's lightness and mobility) even though they have full-frame cameras in reserve.
Cliffnotes: I would recommend getting the T1i and spending a little bit of money on some nice glass for it. The quality of the pictures will be nearly identical between the 2 cameras so then it comes down to the other options. In this case, with the 50D being $940 new (body only) and the T1i being $620 new (body only) that would leave you with $320 for other accessories and glass before you'd even match the price of the 50D with only the body.