In the UK it's still a rarity (don't ask me why - conservatism perhaps), but I get the impression it's more common in the US, particularly because of the geography involved. I find it an excellent tool and in some instances more revealing than face-to-face.
@Martin Most of my initial contacts are though email. Second contact is usually a candidate stepping away from the desk, in the hall, on the cell. I source and hire developers and sales folks. Neither type, unless remote, can Skype at the desk and the worst thing I can do is slow down the qualifying process by waiting for them to Skype.
@Daren. I have to admit I have similar problems, although it's getting much better with mobile devices and the evenings get lost to it too sometimes. However, overall it saves gonks of time and money, and has the added benefit of better candidate engagement.