OT: beischens: TRCPA's post has it right, borrowing shares to short versus naked shorting. MM's I think can "naked short" for a short period of time to "make a market", that is, sell shares they don't have, but have to buy shares to balance out over several(?) days time. An example would be good news on a drug stock and nearly all buying, the MM's "make a market" to satisfy orders coming from your brokers, Fidelity, Scottrade, etc., and fill orders without having enough shares (if they don't have a large enough inventory). Then, over a period of days they have to accumulate shares from sellers "locking in profits" to balance out. They are allowed to do this to keep markets stable, and they can lose money doing it, but they have to keep their customers (brokers) happy to assure future business.
Cash is King until further notice!!!
My comments on companies are usually my opinion of long term success (years). The PPS may go up or down greatly in the meantime depending on the number of greedy suckers with money.