I don't usually wait as long as 3 minutes, but I agree - what to do?? I take a few seconds after all my sets of an exercise to record the weight/reps, and then take a drink of water. Sometimes I adjust my MP3 player. Other times I look out the window, or at the other gym folk. This is when it's nice to have a partner to pass the time I guess.
I like the idea of doing abs. I notice that my gym has moved the stability balls down to the larger weights area (larger in area; we have a smaller one upstairs with some machines that look like medieval torture devices, never have figured them out
). I've also read/heard that you can do abs every day as they don't need the rest - not that I'm inclined to do them that often, I'll skip them as often as I can.