I took possession of my brand new Canon 50D this morning. I've sold my old Canon 1D Mark II N and replaced it with this baby. I wanted a wildlife (and backup landscape) camera with more megapixels (for cropping) and better noise characteristics. I can live with a slower shooting camera, but I'm a little apprehensive about the hit I'll take in the autofocus capabilities. The real test is gonna come in December when the 50D will get a good workout shooting the birds of Bosque del Apache in New Mexico. Until then, I'll be experimenting with it to see what it can (and can't) do.
Update - May 14, 2009: I thought I'd update my impressions of this camera. My biggest concern with this camera upon further use was the noise that it produced all the way down to iso 100. It was just plain worse than my old 1D Mark II N at every iso level! Needless to say, I wasn't happy one bit. My workflow has me using both Photoshop Lightroom and CS3 and upon further research, I learned that Adobe's algorithmns for rendering the 50D's raw files was subpar. The workaround for this was to render them with Canon's DPP software instead of Lightroom. While I hated to have to do this as it's always a pain to change one's workflow, specifically for one camera, it did alleviate the problem. Every time Adobe updates their Lightrooom program I check to see if there's an improvement, but no luck so far.