Wonder if it's just my configuration, but I also found XCode (1.0.1 running on Panther 10.3.1) unstable to the point of being unusable! It also seems to lack the flexibility of ProjectBuilder, e.g. reordering or moving files between build phases.
One of the most annoying things is files I add to my project tend to disappear from it when I close and reopen it.
Can only hope Apple quickly releases a decent upgrade. Otherwise, I wonder what are my options for reinstalling ProjectBuilder on top of the current Dev Tools...