Rand Fishkin: Inbound Marketing for Startups
When asked about paid marketing.  Starts around 74:30"Holy crazy crap does retargeting work.""If you do great inbound, the first money you should spend should be on retargeting... people that were sort of interested but left""...uses a company called has offers in Seattle - they've been very effective for us"."would not recommend raw display.  It will perform poorly for you."