James H.

Sporcle is an absolutely wonderful time sink. There are quizzes on literally any topic conceivable. It's been great as a memorization tool for long lists, and some of the quizmakers are super creative. The main complaint I've always seen is ads, ads, ads. Admittedly, the ads were pretty bad at one point, but they've done better at scaling them back to less intrusive less annoying ones. It's a free site (with no ads for paid members). The community is wonderful to interact with as well.
Admins have been incredibly responsive to any issues I've had, and has always tried to make it right.
All in all, it's been an effective learning tool and a time sink I don't feel too guilty about.