about the crawler ping
 

As the Gnutella specification v 0.6, a crawler Ping, i.e., a Ping with TTL=2 and hops=0, will get Pongs from all its neighours and all its neighbours' neighbours. We want to know whether the leaf nodes of its neighbours will repsond the Ping. If yes, how can we distinguish who is leaf node and who is ultra peer? If not, how can we know how many leaf nodes a ultra-peer have?

Leafs do not respond to pings because they're not accepting incoming connections.

I am wondering how does Limewire gnerate the statistics. Does it mean limewire constantly runs a crawling program and generate new statistic every hour? If so, will this not affect the health of the network? will this crawler be able to crawl the entire network in less than an hour?

"Leafs do not respond to pings because they're not accepting incoming connections."
but is it true that their super peers should act as a proxy and respond with a ping in the behave of the shielded leaf node? for example, if node S is a super node(ultra peer), nodes A,B,C are leaf nodes shielded by the S. Then if i am pinging node S, S will reply with a pong representing itself, and also one pong for each of A,B,C ?
THanks