I actually liked Project Builder, but made the switch to xCode to keep up with the Jone's. The transition has gone smoothly. I am not seeing all the crashes that some have reported.
My application is a straight forward Cocoa ObjC development. My Project Builder project imported nicely into xCode keeping all the build styles. The debugger doesn't seem quite as reliable.
I turned off the auto code completion as it was slow and just wasn't intuitive enough.
One thing I liked about Project builder was containing everything to one window. XCode seems to allow editing in one window, but that's about it.
I don't really see Xcode as an improvement, just a change. So for now I will stick with xCode.
I considered using Java for the development, but the performance was so substandard to the native Obj/Cocoa API's.