Microsoft SharedView (beta)
My friend Chris beat me to the punch on this one, but I wanted to also briefly explore the genius that is Microsoft SharedView (beta). Another Live service in the making, SharedView allows several users to collaborate in real-time via an Internet connection. All it takes is for the participants to install the freeware on their laptops/desktops and a stable (preferably quick) Internet connection.
Within just a few minutes, you can begin collaborating as a team. You have several options, share your own desktop and allow others to view whatever you see on your screen, join another person on their screen, or even take control of you session participants desktop. The participants may hand each other full control of their respective computers. This makes for great collaboration on documents/presentations/or troubleshooting.
Chris, pointed out correctly that a higher connection speed is favorable, otherwise things might get a little choppy. Over a wireless connection you can observe a slight delay (mouse trailing your actual movement by a fraction of a second or so) but over my cable line things are smooth as butter. Other than that, this is an amazing tool that will make group collaboration and communication much more engaging and effective.
For those of you with Vista, try out Microsoft Meeting Space, which is the hosted version of essentially the same product.