Justin.tv internal Hack Day projects
blog.justin.tv
blog.justin.tv
First of all, they have a 20% time similar to Google. 20% of the whole work week can be spent on a personal project, as long as it could be potentially beneficial to Atlassian.
They also have something called a "FedEx" day - the goal is to deliver a software prototype of something in 24 hours (deliver in 24 hours, hence the name "FedEx"). It's a big competition between developers and there's even a trophy for the winner!
Both of these programs have created a lot of awesome features for their software. I think it's something that others should consider emulating...
The obligatory "drive" video:
http://www.youtube.com/watch?v=u6XAPnuFjJc
Disclaimer: I'm going to work for Atlassian soon