Buildbot is used for continuous integration, which is a big step along the path to continuous deployment. A lot of companies are doing this today. Fewer are doing continuous deployment. kaChing has some posts about their setup:
Yeah, it's important to make the distinction between continuous deployment and continuous integration.
Continuous integration is a fairly simple thing: detect a new source commit, run a battery of tests on it, report back. Hudson is a really good one (of which the original author is a main contributor, and I did some plugin work for a while), and I use it as a fairly fancy looking cron as well.
Continuous deployment, as described in the article, is much more difficult. Not only do you have the slew of tests, but maybe you want more long-running tests that you don't care to run all the time. Maybe you want code reviews. You'll need to automate the actual deployment process and so on.
Automattic/Wordpress.com does either automated Continuous Deployment or have their deployments so streamlined that releases are made very frequently and are (almost always) non-events.
