Universities & even residences that may go thru the uni's own bandwidth are tending to block or shape it to stop p2p use. Here's an example of how a p2p bandwidth shaper can work against Gnutella: Bandwidth Shaper Sample (click on link) ie: giving priority to net surfing & low priorities to p2p sharing. EDIT: Sorry that link doesn't seem to work any more!!! Ah .. found it ... they moved it: http://www2.iwu.edu/IT/help/helpdesk/shaper.shtml

It's hard to know whether you're affected by this type of thing or not. You can try different ports or proxies, etc. But some of these shaper programs will also detect the program or protocol it uses.