If it's just a personal hobby thing, I would recommend either going with .Net MVC, Rails or Zend (there may be some good Java frameworks out there but I'm not familiar with them).
I'm guessing that since it's a hobby project, you're not going to want to spend a lot of time looking around the web for examples on how to do things with the framework or looking for tutorials on how to set it all up. You probably want to be able to play with a bunch of cool features right off the bat without things breaking or dealing with a bunch of bugs. That being said, I think .Net MVC and or Rails will allow you to have the most fun with the least amount of headache. With a lot of the other Open Source frameworks out there you're going to have to jump through a lot of hoops right from the start that you would rather not have to deal with, and a lot of the time documentation for getting through the initial setup problems is hard to find.