I have a 350D and a few lens's, I have not had a problem with dust but every couple of months I use the 'self clean' function just as a matter of course.
One thing about the Canon is that you can use the older (red spot) lens's with it which you can buy quite cheaply on places like Ebay. There is a slight difference in focal length but otherwise they work a treat. I am sure Nikon lens's are also interchangeable but I don't know for sure.
The only issue I have is with external flash units, they are very expensive if you want a relatively good one. The built in one is OK for taking pictures of small groups of people but does not rally have the power for longer shots which I used to get with the external flash I used with my EOS.