I am interested to learn from experienced PHP developers about certain aspects of PHP program. We are currently maintain a social game which consists of few mil

I am interested to learn from experienced PHP developers about certain aspects of PHP program. We are currently maintain a social game which consists of few millions transactions every day (through JSON-RPC, not HTML page rendering), and it appears to be CPU-bounded (we use Redis as db backend). Based on my understanding, Facebook is CPU-bounded too and that's the reason behind their custom HipHop. How many PHP programs out there in wild are CPU-bounded in percentage? Because before I got my hand dirty on PHP few years ago, I heard many times that web applications were usually bounded by network/disk bandwidth rather than CPU.