Ah, silly me, got my units wrong.

200 requests per minute, not per second .. about 3 or 4 per second. The instance of LimeWire that was the target quickly buckled (it's not on a very powerful box). Suspecting it was some sort of DoS effort (my other hobby is suing spammers) I checked the router logs. However, the packets all came from one source (claiming to be running LimeWire 3.6.15), and were all valid-looking gnutella packets. To my mind, more the spoor of a runaway polling application than a deliberate attack, hence my post here.