I've been using Skype on Mac OS X for quite some time now and while there are still some minor bugs all the main features work flawlessly.

I've been using Skype Out a long time now and am about to cancel my normal fixed phone because I just don't need it anymore. Skype In has allowed me to link up Skype with the normal phone system and that too works perfectly.

Voice quality is excellent when doing skype to skype calls, skype in and skype out quality is what I'd call "lower mobile phone" standard. Definitely room for improvement there but usually it's not a problem.

Now if they'd integrate video chat for Mac OS X and work on the voice quality I'd be very happy. BTW, Skype works fine with both a bluetooth headset and a logitech usb headset.