More often than not, the process goes something like this: a Daily Kos diarist posts something, which is then on Olbermann the next night. Pseudo-journalistic outfits like TPM start making phone calls, which gives the guys at Politico just enough cover to start get in on the action, making it an MSM story, embroling the targeted Republican and forcing them to respond. In Palin's case, sick Daily Kos rumors were given enough credence to precipitate the disclosure of her daughter's pregnancy, which itself became a pretty big national story.
While you were at CPAC
"In case you're expecting me to bemoan this as the birth of left-wing hack journalism, that's where I part company. This is exactly how an ideologically-oriented newsgathering operation / noise machine / echo chamber should work. The real threat here is not what all of you were booing in Tucker Carlson's speech at CPAC."