It's a way to avoid broadcasting queries, hence reducing Gnutella's bandwidth requirements tenfold. You can read a somewhat out-of-date version of our scheme at http://www.limewire.com/developer/query_routing/. Be warned that the paper is aimed at other developers and is very technical.

The query routing scheme is implemented in-house, but we don't know how it will work on a larger scale. That's why we'll need beta testers in a few weeks. =)

-Christopher Rohrs
Sr. Software Engineer
LimeWire