ON the 7D and 5D series of cameras the weather sealing is ok. I would not worry about a few sprinkles on it, but would not subject them to steady rain or some activity where there is the possibility of a good splashing.
The 1D class of cameras are pretty danged water tight, I've shot with mine for years in pouring rain and on rafting trips not worrying about them getting wet. Of course this all also depends on which lenses you are mounting to the camera, not all lenses are sealed as well as the bodies, this includes "L" lenses. YOu have to make sure your lenses also match the conditions you are shooting in or use covers.
I do also throw covers on my cameras when I know for sure I am shooting in a downpour, but if I get caught without them I don't worry too much.
This is only my personal experience and use, not based on technical things.