[jpdoctor]

> On the other hand: MS also spent ~ $3B providing a floor on Friday by buying up FB shares in the open market.

You don't understand the greenshoe: MS didn't spend a dime. That money came from selling initial shares from the "overallotment". Essentially, suckers who paid too much.

If the price had stayed above the IPO, that money would have gone to FB. Since it dropped below, MS is plowing the money (on behalf of FB) into manipulating the share price.

Edit: My more detailed explanation here - http://news.ycombinator.com/item?id=3996536