You should not purchase a triple-leveraged ETF and expect to hold it forever. Purchasing EDC one time and expecting to sell it at a profit 12 months later is risky because there is no way of really knowing what will happen over the next 12 months.
However, I think that you can make money over time if you purchase equal dollar amounts of EDC at periodic intervals and sell after some fixed length of time (e.g., 12 months later). If you invested $5000 in EDC every month and sold your shares exactly 12 months later, you will make money in EDC if you do this long enough. If the market is really bad, the most you could lose over any 12 month period is 100% of your initial investment, or $5000. However, there will also be some good 12-month periods where EDC rises more than 100%, so you could make more than $5000. For example, if you factor in reinvested distributions, EDC rose from $6.31 on February 26, 2009 to $26.84 on February 26, 2010, a gain of 325%.
If you implement this strategy for a long period of time, I think that your gains will more than compensate for the 12-month periods where you lose money.