I have to say I am quite pleased with this little gem in Vista.  Once I started using it I haven't gone back.  It's a real easy way to collaborate with another user(s) when you need them to see what you see or let them drive your session.  I've used it about a dozen times when I have a TS session and want to look at that session with someone else in the company.  I start WinCollab.exe, create a new meeting, and shoot them an e-mail invite.  They get it, join and I share out my RDP app and we're in business.

 

Here is the step-by-step guide if you really want to dig into it, but its so easy to launch and connect I don't think you'll need this to start using it: http://technet2.microsoft.com/WindowsVista/en/library/8a70907e-9137-4426-a46f-a2d1eeadbd5a1033.mspx?mfr=true

 

Check out http://blogs.technet.com/james/archive/2006/10/20/view-on-vista-windows-meeting-space.aspx for a nice little video on it.

 ***UPDATE***

If you cant connect to someones meeting make sure that both of you have ipv6 enabled.  If you disable IPv6, you will not be able to use Windows Meeting Space or any application that relies on the Windows Peer-to-Peer Networking platform or the Teredo transition technology.