Don't Buy Ultras!
Disclaimer: This is not aimed at those who trade ultras responsibly.
The only sure thing in security analysis, to me, is the ability to determine at this moment whether or not a company is overvalued or undervalued. A solid strategy, then, would be to go long undervalued companies and short overvalued companies.
If you're going to buy something like FAZ because you're sure the financials are going to collapse, you're playing a dangerous game. If you don't get the timing exactly right, you may want to hold longer and longer. Holding something like FAZ "until you're right" can decimate your portfolio pretty quickly. A smarter move would be to short FAS if you can find shares, since the decay will at least work in your favor. However, I still don't recommend that move either in real life.
A good quote I remember is something like this: "the only certainty is in what direction the stock's price will go, not the timeframe in which it'll happen." With something like FAS or FAZ, if you're wrong about timeframe and correct about the direction, you may go broke before you're correct on your call, if the market decides to stay irrational for a while (which happens all the time).
My suggestion? If you truly believe the financials are going to collapse, short a basket of financials. One of the problems with heavily shorting one company is that it's ridiculously risky at times. This is alleviated by shorting the basket.