All in with Xcode4

I've jumped on the Xcode4 bandwagon.
One word of caution, if you are using Hudson (now Jenkins?). Don't uninstall your existing Xcode3. Just 'move' it:

$ cd /
sudo mv Developer Xcode3

Now with your existing Hudson build environment, alter the builds to use /Xcode3/usr/bin/xcodebuild.

When you install Xcode4, it will install itself into /Developer, and you can begin playing with making Xcode4 projects auto-build with Hudson CI.