I have one, but there isn't really much you can do except bounce. The surface space isn't wide enough to do much else.
I tend to do a combination of big bounces, small bounces and kind of jogging on the spot. I expect there are other things you can do, as I know some gyms run "Urban Rebound" classes, using a mini Trampoline, these classes must consist of more than regular bouncing.
I also sometimes hold light hand weights (2kg) and do shoulder presses, front and lateral raises and biceps curls, whilst bouncing.