I had an RB for several years, I loved working with it but it was usually a tripod camera for me. One time I mounted the RB (with grip) on a monopod, and managed to break the mounting screw off in the base of the grip... I guess this was from subtle twisting on the (cheap) monopod. It is indeed a heavy camera.
A friend of mine has a GS1 with the speed grip, I've played with it a little and it is a very sweet camera.