I've got nothing against POB, but there's several simple facts to keep in mind:
1) It took Perkins FIVE YEARS to be the serviceable center he is today. (I like Perk, but that's still all he is.) So don't expect C.Ray to perform miracles overnight.
2) #1 above is made worse by the fact that POB will not get much playing time, at least not right away. (This was also part of Perkins' problem early on.) He certainly is not ahead of Leon Powe in the big man rotation and probably not Glen Davis either. He might be used in very select situations like against taller centers (Z, Yao, etc.) but otherwise will ride the pine.
3) POB should have shown some potential by now. I applaud him for waking up to hard work, but I really don't see the necessary talent.
It's very possible that POB shows steady improvement as a Celtic and then becomes trade fodder down the road, just like Delonte West, Ryan Gomes, etc.