Here's what I found:

The major improvement in 3.6.0 is the use of "out-of-band" replies to your
searches. This is pretty technical change, so I'll describe it in some detail.
Here's how query responses worked prior to 3.6.0:

When you sent out a query on Gnutella, anyone who received the query and had
responses would send those responses back along the same route that it came,
i.e. it would send it back through every LimeWire that had originally forwarded
the query. This is inefficient because the LimeWires that would route the
responses could be on opposite sides of the planet, forcing the LimeWire network
to do much more work than necessary to get back to the querier, even circling
the globe multiple times!

With LimeWire 3.6.0, however, those responses will be sent directly back to the
querier instead of being sent along such an inefficient route. This allows those
queries to be sent back by extremely high performing IP routers that will always
clobber LimeWire's network topology in terms of performance.

The result of all of this is that the responses will get back to you much more
quickly. You will especially see a speed improvement with queries for rare
content because these queries travel further out on the network to get their
results than queries for popular content. As a result, they have a greater
distance (or number of "hops") to travel to get back to the original querier.

Hope this helps. This feature was added several versions ago, as you can see.

Dan