Be careful with the 50D's, I bought one new and it had a problem with the sensor that was only showing up during long exposures (astro imaging). I took the issue up with Canon Aust twice an they refused to admit it was a problem, therefore no warranty repair
Essentially they left me high and dry, they were also suggesting that I should stop using the camera for astro as it wasn't designed for that application. However, on the upshot it was fine for daytime terrestrial photography.
Interestingly I got my hands on a second 50D body and it's perfectly fine for astro imaging, no problems.. So it just goes to show that I was right when I was originally trying to get Canon to see the problem with the first one.