I've called aus. with it. The phone call quality is better than a phone if you get a decent headset mic, and by decent I mean roughly 10 quid. The PC to PC quality is slightly better than the phone quality, mostly because there is no phone involved (headsets have better speakers and mic than a phone does). Of course this presupposes that you have a fast connection. At least 2mb down, and .5mb up.

However, for PC to PC voicing, I still think MSN msgr has a slight edge. It's not a huge difference (since skype's last update) but I still think it does have a slight advantage.