George Schlossnagle - Why PHP Scales - A Cranky, Snarky Answer:
"In every application I've ever worked on application performance was governed by the following factors, in rough order of their importance:
- stupid use of network resources
- stupid use of databases
- stupid algorithm design
- stupidly ignoring contention issues
- stupid language inefficiencies
Notice how PHP being naturally slower than Java (something I believe to be true) comes in last? That's a distant last."