The built in Windows Remote Assistance in win 7 is fucking awesome. I was trying to help my uncle with his PC over the phone... eventually I had enough and had to do it for him so I asked him to open Windows Remote Assistance, all he had to do was click 'allow someone to help me' he gave me a unique code, I typed in the code and it connected me up and straight away it was working. Didn't have to install anything, sign up to anything, mess with router port forwarding etc.
Another win for microsoft. I do actually use VNC though for accessing my PC from my iphone.