[marvin]

Even the best case wouldn't have you more than double your money, if you put up 1:1 collateral. I guess you could have less collateral than this, but in that case, given a growth stock, you would be wiped out if there was a modest increase. I don't see the risk/reward curve for long-term shorting.

[mortehu]

When the price starts dropping, you would have to sell more shares to maintain a 1:1 ratio. For example, you can double the number of shares each time the price drops by half, and make up to 200%.