Twitter uses Java. It seems to survive major events fine these days. I'd say it scales reasonably. You also have to take into account huge enterprise deployments.
As for 'fast' it really depends what you mean. Nobody's going to dispute that running a compiled application written in C is going to beat the pants off anything running on top of a VM, but is that speed factor important all of the time? Of course it's not. Most of the time a short wait is perfectly tolerable in exchange for the assistance in writing correct code that languages like Java can provide.
As for 'fast' it really depends what you mean. Nobody's going to dispute that running a compiled application written in C is going to beat the pants off anything running on top of a VM, but is that speed factor important all of the time? Of course it's not. Most of the time a short wait is perfectly tolerable in exchange for the assistance in writing correct code that languages like Java can provide.