I use toe cups because I'd read about foot retention and the potential benefits (particularly for climbing). I really didn't like the idea of being strapped in completely, and toe cups seemed like a gentle introduction. As it happened, I really liked them, not so much for pulling up (which apparently is a bit of a myth anyway), but because they give me the idea that whatever forward force I apply to the pedal, actually gets transferred to the drivetrain. I suspect most of this is in my mind though.

The real reason I stuck with them is that they help in keeping your foot on the pedal. Not that I have a problem in that area, but they make me feel more secure bombing down hills. If you hit a bump at 30 mph, it's nice to know that your foot will stay on the pedal.

I put toe cups on my wife's bike as well, and she really likes them as well (pretty much for the same reasons).

I'm still kind of interested in potential benefits of other types of foot retention, but I'm still weary of being strapped in completely.