There's nothing sillier than trusting unsourced information from entirely anonymous Internet sources, but I can't help but mention the "Enron/AEP bribery recordings", which will probably be revealed as fake pretty soon, but which are otherwise rather interesting. The 'silly rumor' half of the story is that a private investigator working on an unrelated case tapped the phone of an energy executive, and managed to record some discussions of AEP paying off key employees with $5 million bribes to cover up accounting irregularities. The 'could be something to it' part is that there are several sound recordings, allegedly of these conversations, which you can find here, here, and here (bittorrent users can get the complete collection here).
Whether or not it's true, this could make an interesting case study in how quickly information spreads: As far as I know, it was first posted at about 10 PM ET; since the recordings are already available from several sources, it's likely that at least a few traders will hear about it by the open. Now, if we want to know whether sophisticated traders have faster information sources than everyone else, what we'd look for is high options activity: If you intend to make money on a short, unexpected swing, buying puts is just about the only way to do it. The volume in AEP options is minimal, so any sudden action should definitely show up. Granted, a few low-fi recordings of someone who could easily be an actor shouldn't be worth more than a percentage point or two of lost value. But there's a point at which the effort involved in making a practical joke -- coming up with the story, getting plausible voice actors, making and spreading the file -- is so high that someone out there might find the story plausible.