Quick tip: Uninstall Xcode from your Mac
So, today I need to install Xcode 4.1 after installing Xcode 4.2 beta 7, but apparentlly it will not “downgrade” the new 4.2 beta version. So, I came to the conclusion that I have to uninstall the new Xcode 4.2. Apparently, just deleting the Developer folder won’t cut it. I found out that the correct way to uninstall Xcode is to run this command in the terminal:
sudo /Developer/Library/uninstall-devtools --mode=all
Hope it helps

i tried it. reinstalling now.
curious if java and certificates will all be flushed out.
looks like they were not, and all sample data i downloaded is there too.