Until a couple of months ago I'd never bought CD keys before, and was a bit hesitant to do so. But CDKeysDirect's prices for Mass Effect 3, and now Diablo 3, were a big motivator. I was saving maybe $30 compared to directly buying online.

Anyway, the keys arrived quickly (Diablo 3's arrived the evening before launch) and worked both times, so I'm quite happy to buy from here again.