"The so-called borrow rate, or fee imposed by brokers on traders who want to sell short, has dropped to about 30 percent from 99 percent earlier in the month, Leung said. At 30 percent, Groupon’s shares would have to decline by at least that much before the trader makes a profit."

I must be missing something...

When I buy shares, I don't get to inform the broker that the stock needs to go up by 30% before they can execute my trade at today's price.

Betting on a stock to dip 5% seems like a big enough risk that I should be able to make money on it. 30% just sounds crazy.