The Open Quickly feature has surely improved, but it is in need of further improvement. The new implemntation still does not allow searching substrings. In most cocoa projects one has same prefix on almost all files, so writing it is quite useless, and in may cases finding the files ending "Additions" or "Controller" would be the quickest way to filter the list and go to the wanted file.

I and others have submitted this to Apple as a bug. Hopefully it will be in Xcode 3.2.