I also consider the Facebook requirement obnoxious - up until I decided to give Grouper a spin, my Facebook profile was minimal, not even a profile picture. But I was curious enough that I bit the bullet and gave Facebook way, way more information about myself than I'd normally be willing.
Which, of course, makes the vapor nature of the service that much more upsetting.
My experience could very well be an aberration - that said, I figure I'd throw out a warning to others interested in trying to service but are hesitant to give Facebook more personal information.