A couple days ago, Dustin Sallings, the other of the spymemcached Java client for memcached, posted an article on some optimizations done to the library. If you are currently using hibernate-memcached you may want to try out the latest spymemcached RC release.
If you combine the latest spymemcached RC release, with memcached 1.4 and the new binary protocol you should see significant performance increases. As Dustin didn't change anything about the spymemcached API it should be a drop in upgrade for you.
spymemcached Optimizations - Dustin Sallings