I just ran across this tool, and it's great for sharing your desktop to a bunch of people at once... and the good news is that they do not have to install anything! All they do is go to a web site to see your desktop. With Join.me you download a single program, run the program and then give your colleagues the URL you’re given. When they follow it, they see your desktop. Live. It’s as simple as that. Awesome for doing a webinar type presentation.
If you are doing a one-on-one computer support session, I still recommend Team Viewer. http://www.teamviewer.com But this program requires more installs and downloads and is designed for only peer to peer connections, unlike the Join.me product which is more for the one to many presentations.