Why should I jailbreak my AppleTV 2G?
Other options are installing XBMC or Plex, and having much more control over your Apple TV - you can then play any media format, more easily access data from your other computers, access the full internet (as you pointed out) and find lots of different plugins for a range of different things.

If you are interested, you can check out this article on Lifehacker about jailbreaking and installing XBMC - it's really a very straightforward process.

If you'd like to have a play around, you can also download XBMX and Plex for your Mac or PC to see what they are all about. Good luck.