Check that your ISP hasn't started filtering p2p.
There are a few tips in this thread, follow LOTR's advice
http://www.gnutellaforums.com/showth...download+speed

You can try downloading a magnet link & see what speed you get. Link is here
http://www.gnutellaforums.com/showth...ht=magnet+link

Providing you haven't made any changes to your set up (new hardware etc), I'd suspect it was an ISP issue.