Another trick is to use a very high speed server connection and high speed CPU and put up a modified Ultrapeer/Supernode to capture as many connections as you can and not return any search hits, or only "approved" filtered ones, meaning no MP3s mostly.
This would effectively lock a leaf node into that Ultrapeer, since it dropps all other connections, and then play "censor" as they see fit.
If enough nodes get sucked in (could be 10's of thousands times as many servers as they can put up) they could censor the whole Gnet.
Need to think up a way to detect and stop this, a central trusted IP based black list would be a good start, but they can move their servers around or other tricks to get new IPs.
Another idea is to always connect to a few other non Ultrapeer nodes no matter what.
More ideas?