Shorting BHP now coud be very dangerous, you've already missed some serious action and any positive news could see a run to test $40 very quickly. On the short side i always try to stick with highly leveraged stocks that don't pay dividends. Having said that i think the market is a little short term oversold and i'm not adding any more shorts at the moment.
Ps: BHP is getting shorted because people are worried about the new tax, but is it really a good idea to short a company because it makes super profits?