Ok a couple points: First, if your goal is to freeze action, IS gives no benefit whatsoever. If, however you like the type of club shots where the photo shows movement (on the dancers part but no camera shake) then IS can be very beneficial. So, it depends on what your goal is.
I don't have an IS camera myself, but I'm not understanding your conclusion here. If having IS gives you a 2 stop slower ability to hand-hold the camera, how does that not conversely affect the ability to set a faster shutter speed to capture more action-oriented shots?
I guess my understanding is that focal length, shutter speed and ISO all work in conjunction with one another, so how can IS be helpful in one instance and not the other?