For Yelp it seems like it's more of a failure to innovate and grow beyond their initial review site concept. The idea was good, but easily challengrd by others who bring additional utility to the table like OpenTable and Google Maps.
I don't see it that way. It's a review site. There is no need for it to innovate beyond that, nor is there any basis for thinking that reviews should be enough to take a company public.
If they're doing that, then you know that the end goal is ads, ads, ads.
