I finally upgraded to the GM seed of Xcode 4 today. It's a bit of an adjustment process as usual, but so far I really like what I see.
One of the biggest annoyances is that Xcode 4 doesn't automatically take many of your Xcode 3 settings during the update. Most egregious is the lack of theme compatibility. My favorite theme is the Zenburn theme (I use a similar theme in Visual Studio).
I've taken the liberty of converting the theme to Xcode 4 format and posting it for download here. Enjoy!