<i>With HipHop we've reduced the CPU usage on our Web servers on average by about fifty percent, depending on the page.</i><p>Hmm. I'm guessing they're comparing it to their PHP stack that has already had the living daylights optimized out of it (with cached bytecode, etc.) and/or a large proportion of their pages doesn't hit much code (lots of stuff cached?). I'd have thought there would be more mileage in this.