I run a PC gaming website (wsgf.org) and we have Admins in several countries (2 in US, 1 in UK and 1 in AUS). We've used Skype okay, but the video would cut out some. We tried a "con call" with our larger Editor group (several each in US, South America and Europe).
Skype crapped out on us, even with just voice. It was unusable. We have a Mumble server for gaming groups that get together. We all got on and it was perfect (outside of my newbiness with the software).