I've had two interesting things happen to friends computers over the past few months.
First I got an email from my friends at Tin Roof (by the way, if you want to support a great charity... this is it) telling me that she needed to file an extension on her taxes before she leaves for Nicaragua on Tuesday. However when she started Turbo Tax she was getting an error.
Further investigation by me (via a VNC connection I set up with her a while ago) realized that this was a .NET error.
Turbo Tax spit out the following error: 20888 39915. A Quick search of their site gave this article. Basically blaming .NET and their solution has a link to a program that totally wipes out .NET from your system so you can start over. I downloaded the program, ran it and then reinstalled .NET and her problem was fixed (well after I ran a reboot.bat file that was in the Turbo Tax installation folder, but that's another issue all together).
Then I have another buddy who had been using a program I wrote for my church to transfer files between members of the multimedia team. Several months ago a basic Windows component of it stopped working right. I was at a total loss for a solution (as a simple uninstall and reinstall of .NET didn't help). I let it drop... but I emailed him today with this fix and my hunch is, that this will get him up and running again.
What frustrates me the most about this, is that Microsoft's .NET uninstall doesn't fully uninstall itself. Many years ago I did some work for Lexmark's All in One printers and one of the BIG things they did was make sure that their uninstall completely wipes out any record of the machine being on your system. And really there is no excuse for any other behavior.