irvine_grad,
It isn't the shorting that artificially pulls up the price, it is covering the short which requires buying. You are essentially correct in that it is the high short interest which is creating this volatility. When one person covers, another shorts the top of the rally, and the cycle starts all over again. It will take major institutional buying or selling to make a sustained move. Many of the institutions have already exited, and many others are taking a "wait and see" approach right now.
acpme,
I think the high level of short interest in the homebuilders caused their recent rally off the bottom. Like you said, if everyone is already short, if there aren't any big sellers to take the price lower, the shorts must cover, and a rally springs up out of nowhere. I suspect there are still many big institutions with shares they need to liquidate.
muzie,
Unfortunately, I think the "too obvious" problem has spilled over into put options on the Alt-A lenders. In an ordinary stock, the price of at-the-money puts and calls are approximately equal with a slight premium for calls. I checked the prices of puts for IndyMac (NDE) and the premium for puts was double the price of calls. I have never seen this phenomenon before. To make money with the premium that high, the stock price has to collapse. Anything other than a total collapse will be lost in time premium. Personally, I had thought about shorting these puts to make the time premium, but chose not to because the possibility of complete collapse is real -- just not real enough to give me confidence to go long on those puts. Good luck with your trade.