A quick heads up for anyone working with Ubuntu 12.04 (or above) and reading/writing files to /var/run (e.g. pid files, sockets) for processes/daemons/init scripts and the like.
The "run" directory has now moved to /run at the root of the filesystem - in the case of Ubuntu 12.04LTS there is a symlink from /var/run -> /run to ensure existing packages/scripts don't fall flat - but probably not a bad idea to start using /run as a rule of thumb going forward for your code/scripts.
From memory, Fedora (and possibly others) have made this change - please let me know in the comments and I will update the pro-tip.
Enjoy your /run-ning!