The internet on your PSP
It's a great feature but it is incredibly hard to type. If you don't know what the typing is like, it's like typing on a cell phone. Just typing this sentence alone will take 1-2 minutes.
It's fun to use but you are still better off with a regular computer. It's very useful, but some sites, like GameSpot, unfortunately take over 10 minutes to load, when on the computer it only takes 10 seconds.