Of course it's more complicated than that, but let me give a simple example of the opportunity. GM currently trades for $4.00. The June 2009 $4 strike put trades around $2.30, and the $4 strike call at $0.80. You can put on a June forward position in GM via options, by buying a call option, and selling the put.
Looking at Put-Call parity, we can generate the following implication. A synthetic forward position can be created by buying the call and selling the put:
As interest rates are near zero:
Call-Put=Forward - Strike
$0.80-$2.30=Forward - $4
Now, if you are a long term investor, why pay $4.00 for the current GM, when you can by the June forward for $2.50? If GM goes up to $5 in two years, one makes 100%, the other, 25%. The dominance of the forward doesn't get much more obvious than this.
Anyone long GM who is not capturing the huge negative rebate is leaving a lot of money on the table. They must be dancing over in Staten Island, as stock loan desks are living large because I imagine many if not most GM stockholders are not capturing this. If you like GM, buy a forward via options. If you dislike GM, know that a 50% decline is baked into the current stock price via the un-labeled stock rebate.