Last month, I wrote a post about migrating .NET 1.1 applications to .NET 2.0. My colleague Doug Turnure put a handy little slide deck together based on the information in that post. I've updated the original post with a link to the slide deck. It should make a nice reference to keep around.
Now that we've got the confusion out of the way about going from 1.1 to 2.0, I'll have to look into writing a post on how to migrate from .NET 2.0 to .NET 3.0! Given that 3.0 is essentially an 'add-on' to 2.0 with the Vista technologies (WCF, WPF, WF, and WCS), I'm hoping that there is no "migration" work to do to get on 3.0. Of course, you'll have to re-factor your apps if you want to take advantage of the new features!