I think another important point to add to this as we throw around (myself included) speculation of shorts raining on the parade, is that there are very few brokers (Interactive brokers is one) that will allow you to short pinks and OTCBB below a certain price (I think it's below $1). The ones that do, have insane margin requirements. For example to short 1000 shares of a $0.01 stock you need to have $2.50 margin buying power PER SHARE. The reason for this is that .01 stock could jump 1000% + in a single day. Huge risk shorting pennies and not many people have the capital to do it.
Short answer is it does not pay to short pennies and not many people can and do.