Thanks Wolfster - it could be interesting.

I've thought about shorting the ultras, but I have a better idea - sell calls. Because of the high volatility of these things, premiums are high. If it gets assigned, you can sell a put and collect another premium. If the put gets assigned, you're out - with 2 premiums in your pocket. Selling calls should work over the long haul, because these things are almost guaranteed to go down over time.