This thread is very interesting to me. I mainly use BeamYourScreen (aka Join Session, aka Mikogo) and it's pretty good, except that there's no VOIP which I could really use.
The main issue with other desktop shares (from my point of view) and why I have stayed with BYS despite the expense, is that there's no way for a participant to show you where they are pointing with their mouse. In BYS, if Fred and Joe are viewing my screen, and Fred clicks somewhere, I see a big arrow marked 'Fred' so I know where he's pointing. It's amazingly useful.
Does anyone know of other services that support this seemingly simple but essential feature?