At bitly we follow a process very similar to github. One difference though is that we structure things internally as smaller services, and as a result we do deploys to smaller groups of servers at a time. Deploys for us are the one way we do state changes on a machine. This means that it encompasses more than just the code we write, it's also all of our configuration, system installs, crontabs, monitoring, you name it.
Deploys are done through an internal web based system, and are run by nearly everyone that commits to our repository (designer, developer, or ops) and can be run at any time day or night. We have put a lot of effort into being able to do zero downtime deploys for almost all of our systems, and as a result we've pushed 8156 deploys in the past 12 months.