Yes I have one and use it inside and out. It's ok, but I made the mistake of buying a mid price range one, think it cost about �30. it doesn't give me alot of bounce and after using it, have really bad lower back pains.
It's a good form of cardio exercise and supposedly low impact and can help to tone the lower body. I use light handweights as well, whilst bouncing, to do biceps curls, front and lateral raises, so my upper body gets some work too.
If you are going to buy one, you should probably try it out first in a sports store if you can, and make sure you get a good quality one.