Wow – that’s a heck of a traffic spike! Here’s hoping he gets some additional readers from it!
Will the $mutex fix check for old locks (can that even be done efficiently?) I got nailed by a hung mutex lock on a wp-cache file, which slowly locked up web processes waiting for the lock to clear, eventually shoving me into my max virtual proc limit – suddenly my sites are returning 500 Errors!
Definitely think it’s time to make the switch regardless – your new cache plugin looks great.