So I had Visual Studio 2008 beta 2 installed and got my copy of the RTM media from Ryan today, so obviously I had to do the upgrade today. However I did have Ryan warning me of his experience with it (what made it worse was he didn't even have the beta installed). So I uninstalled the beta. Popped the disk in and it told me to uninstall the beta .Net 3.5 framework. Did that, ran the setup again and it worked, perfectly.
Dunno what else to say really. Normally these things are ammo for the annoyance tag but not today! However if you are unlucky like Ryan, read his post as he is getting some lovely info from MS on the comments.