Mediaforce and Overpeer claim already to be flooding the gnutella network, - and I have no reason, not to believe them. The networks efficiency has clearly decreased in the past months and some searches only return 20-30% of the search results you would receive early this year.

PS: The methods described in the paper DO work, - despite the fact that it's 6-8 months old. Those security issues have been known for a while and the age of the papers it links to has not much to say. The gnutella network didn't change that much over time. GUESS, however, will solve some of those problems.