It looks like PMs where being silently thrown away for almost two week (since 17 Nov 2011).

Things are back to normal as of ~1500 PST on 29 Nov 2011. I have personally notified any users that tried to send a PM during this time but have no records of who their recipients were. So if you sent a PM in the last 2-3 weeks and got no response, please blame me and not the recipient of your message.

Best,
Ian