Upon Julian's urging (and after having been sniffing around the idea myself for some time, too) I've installed Skype. My username is martinsutherland, because the signup process told me that "sunpig" had already been taken. Being curious, I did a search for the name once I got the program up and running, and found...no such user. Harumph.
Oh, and just like Instant Messaging, don't expect to see me online in your contacts list very often. Showing up as online only encourages people to try and contact me, and why on earth would I want that?