Three finger gestures are awesome in Xcode, but they disappeared in Lion :(
You can bring them back to life however...
Inspired by a post from @gordonhughes (http://geeksinkilts.com/?p=67), explaining how to bring them back on an external trackpad, I started digging around for a way to get it working on the internal trackpads for the mbp/mba models.
Perhaps an easier way of doing this found by @gordonhughes again is just this 1 line in Terminal, haven't confirmed this yet though
defaults -currentHost write -g "com.apple.trackpad.threeFingerVertSwipeGesture" -int 1
1. cd /Users/USERNAME/Library/Preferences/ByHost // replace with username
2. ls -lah // will list files, you're looking for a hidden a file name something like this unique string .GlobalPreferences.XXXX-XXXX-XXXX-XXXX.plist
3. open -a /Developer/Applications/Xcode.app ".GlobalPreferences.XXXX-XXXX-XXXX-XXXX.plist" // replace filename with your file
4. this will open the plist editor in Xcode, set value to 1 for the key "com.apple.trackpad.threeFingerVertSwipeGesture"
5. Check there are no gesture clashes in System Preferences
6. Restart the machine