LOL what a question. I used to have an XSi (it was my first DSLR) but since I'm a gearhead, I upgraded it to 5D (for 2 weeks), then I realized that 5D wasn't what I wanted (note the word "wanted" I don't need any DSLR, it's just a hobby)...
I primarily shoot anything everything but I enjoy shooting wildlife and sports most. And, 50D seems to fit me best. Thus, the short ownership of 5D.
I bought 5D used locally to upgrade from the XSi. I used it for only 2 weeks and I realized that I need all the reach from the 1.6 crop factor I can get. Don't get me wrong, 5D was awesome. But I have a Sigma 70-200mm, which is 70-200mm on 5D but 112-320mm on crop bodies.
Additionally, I still own 3 APS-C lenses and it'd be too much of a hassle for me to totally revamp my lens lineup. I'm lazy like that
I guess bottom line is to go with full frame if you like portrait and landscape and crop body if you like wildlife and sports.