It doesn't even take a billion hits. I'd say it's a problem as soon as you scale to a couple dozen servers. At that point you're wasting enough money running extra cores that you could have hired another dev instead. We picked up something like 6x web frontend performance by doing a pretty straightforward if tedious Java port (64-bit Sun JVM), and it also put us in a position to start using NIO (with Netty) much more heavily.
