Yeah, exactly.  The reality is that most web applications don't handle IO sanely, and have a 100-400MB process sit idle while waiting for the results of a database query (or for a slow client to suck down the rendered page).<p>Using a proper threading system (and I mean lightweight threads, not OS threads) makes any application CPU intensive instead of IO-intensive.  If the app doesn't use all the CPU, it's performing as well as possible.  If it does use all the CPU, then making it run faster is a net gain for your users.<p>This is PHP, though, and you would have to jump through a lot of hoops to remove the IO overhead.  At least HipHop uses libevent, so at least apps won't be blocked by slow clients anymore.