I've been running this on OSX, Linux & Windows under both Rubinius and JRuby for the past few days. So far I have not encountered any obvious bugs.
I would like to point out that it's surprising that ReplSetConnection's "refresh_mode" no longer supports the :async property. Was the background refresh a source of the recent problems? It had just been introduced a short time ago, so to see it disappear already was a bit surprising to me.
cr