Had problems with lagginess. End up talking over one another. More participants makes it worse. To be fair, this is with the free service accessed by going to free.gotomeeting.com/PICKYOURPATH. Easy to share though and good for quick impromptu's.
Gotomeeting is easy to use especially in combination with the chrome extension that schedules meetings right from your Google Calendar. We use it for demos and sometimes support. One drawback for support usage is that it doesn't support copy/paste in interactive sessions.