IR sensors played a huge role in the most satisfying FRC match I've ever had the pleasure of participating in. I've even got the video to prove it!
In autonomous mode of
this match we (the robot with the red bumpers) picked up another robot with those
Sharp IR distance sensors. I'm pretty sure that's the exact model we used on that robot. Either way, I've used a few of the models and in my experience they work equally well. They were statically mounted, we turned the robot. We've experimented with mounting them on servos, but as always, we run out of time. A word of caution though, IR sensors will not see polycarbonate (Lexan) unless they are pointing directly at it (the "beam" is perpendicular to the Lexan). They also are not very reliable at seeing particularly shiny things (think polished diamond plate commonly found on FRC field). Those are our experiences anyways!
We've experimented with the MaxSonar sensors. Those also work well.