I don't have the 50D, so I can't speak to that, but I can say that I absolutely love my 1D MkII!!! I have a 20D which still works perfectly, but has now been relegated into the spot of backup body. The click of the shutter on the MkII is a beautiful sound; even my husband notices when I've picked up the 20D to shoot with, as he asks what's wrong with my shutter? It sounds so plastic-y Then there's the second shutter release for when you are holding the camera in either the horizontal or vertical position-it can't be beat. I shoot high school football, and that feature alone helped me capture numerous shots which would have been missed if it had taken me even a split second to hunt for that shutter button.
It IS built like a tank, and I really don't give it a second thought when I shot in inclement weather. Yes, the dials take some getting used to, and it does feel clumsy rather than intuitive when you need to change settings; but once you're used to it, it's not difficult at all.