What happened with Facebook’s IPO was unprecedented, not because of the size of the offering (though it was certainly the largest ever offered), but because of some questionable matters concerning who knew what, and when, and what they did as a result. Henry Blodget gives an excellent rundown of the events. It’s particularly helpful for those of us who aren’t familiar with the conventional industry practices surrounding IPOs, and therefore might not realize just how far Facebook’s IPO deviated from that standard. So what happened, exactly? Facebook held what is known as the IPO roadshow to dru…