No word yet on exactly what drove Yelp to back down, but there are really just two main possibilities here:
• Yelp was uneasy with whatever Google's plans for their company were. Given that Google already has a Yelp-like service in Google Places, there was a good chance that their plans would've involved cannibalizing Yelp for review data, or at least subordinating the brand for something more Googly.
• Yelp got a better offer, or at least the sense that they could get a better offer. Not that many tech companies could offer more than $550m for something as ephemeral and low-revenue as Yelp, but of the ones that could, nearly all—Microsoft, Yahoo, Apple, Aol—are locked in one war or another with Google. Even if their plans were never firm, there are a lot of powerful companies with a vested interest in Google's local reviews staying somewhat lame.
So Yelp will keep Yelping, just as it has been Yelping for the history of Yelp, for the foreseeable Yelp. Let us know if you hear anything else. [TechCrunch]