I use this daily with my dev team. It's great because skype is cross-platform, easily traverses firewalls/NAT, and combines the screen sharing with voice chat.
Any competing tool (or set of tools) would have to accomplish those same goals.
Also, I tend to use skype (or email) whenever I have to paste a large block of text (like a stack trace), since Yahoo and AIM both avoid sending messages if they're too long.