What Nikon rig is he looking to trade? The 50D is a great camera, and the lens with it is also great. It has a fast shutter rate, high megapixels, and millions of other great specs. However, if you've been a Nikon user for your entire life, it's a tough switch to Canon. The thing is, you won't be able to use your Nikon lenses on your Canon, and you'll have to learn new firmware, hardware, and every other type of "ware" that is different in Canon.

If the person is asking for anything more than the D300, DO NOT TRADE HIM! But, honestly, either way, I say stick with Nikon.