[inkista]

Why do you want to trade the 500D in? would be my first question.

Chances are good that any "upgrades" to one-higher-tiered bodies in the same generation aren't going to net you a ton of image quality improvements, just better features/build. The 500D and 50D more or less share the same sensor and processor. Noise performance is actually slightly better with the 500D, because it came out later and had more tweaks to its noise processing. It has video and the 50D doesn't. So, if you're going to upgrade, make sure that it's because of the features the 50D has that the 500D doesn't. If you just assume you're getting an overall upgrade on everything because of the prices difference, you may be disappointed. The general advice is that upgrading a single generation in the same tier, or one tier in the same generation often isn't worth it.

Also, product announcements are due next month, and chances are good that a 50D successor will be announced. Might be worthwhile to wait and see because if a 60D does happen, it's likely to have some 7D features in it, most likely including the 7D sensor and processor. With maybe a few tweaks.