Been cranking on a new project. A coworker asked if I had SharedView when we were doing some knowledge transfer. I'd never heard of it but downloaded it and finally got a chance to try it out last night and it is AWESOME. If you regularly get calls from relatives that start off "I'm on my computer and I'm trying to...", you NEED this utility. Where "Remote Assistance" falls flat on its face, SharedView shines.
We used it last night to track down some code issues. The session host is able to share a single application or their entire desktop to all other participants (up to 15) in their session. Initially the session host controls the mouse and keyboard, and other participants get a color-coded read-only mouse cursor. When read-only participants click on things, it draws a circle around their cursor to draw attention to it. The session host can easily hand over control to another participant (and just as easily take it back). There's "handout" functionality if you need to exchange files and it has minimal chat functionality, but we mostly used IM to talk. I was hosting the session, but the other participant said performance was fast when viewing, and a little bit slower when controlling but nothing major.
Most importantly, setting up a session is pretty painless. It automatically generates a random password for your session and populates it into a link you can IM/email to other users to join in. That's about all there is to it. Like most everything Microsoft now-a-days, it does authentication based on a Live account, so you'll need one to have one even to just to watch a session.