Freshbooks"Hack Off" day

Mike over at the Freshbooks blog, FreshThinking, wrote an interesting post.  It’s about how they take a day, typically once every couple of weeks on a Friday, and the developers work on whatever they want.  The stipulation is that they be done by 4:30pm and show a demo to whoever walks by.  They call it a “Hack Off” day.

I like this idea and the spirit behind it.  The demo is of course the key piece.  Otherwise few projects would be done in a day.  It’d be fascinating to see what people work on.  I know I personally have a long list of projects that could probably be nudged along decently in one full day of uninterrupted work.
Uninterrupted, of course, is the key.  How do you make sure people don’t interrupt each other with issues from the current Scrum sprint?  Support issues?  The random feature request walking by?  The costs of context switching are so high that interruptions really screw everything up on a one-day project.