I recently came across a Kickstarter project called BOLT. I spoke with the creator and he has informed me that if the power were to go out the battery would kick in immediately. So for those of us who have been looking for a good backup battery solution for the Raspberry Pi, this one could be good!
Edit: I received my Bolt today and you cannot use it as a backup solution like I was lead to believe. It is a beautiful charger/battery backup though!