Sure, but it's also important to realize that Google Maps was a rare success in a string of mostly failed projects/acquisitions (Orkut, Knol, Picasa, Google Video, etc).. I'd argue that Google's biggest successes were in areas in which the previous leaders failed to innovate for years (Mapquest, Hotmail), whereas Yelp is a very active company in a constant state of improvement/innovation. If I were Yelp, I'd be more concerned about Google doing something which would cause it to lose placement in search results.
Yelp is, from my observations, anything but active. They haven't innovated in terms of UI or features in probably two years. Even geographies have been slow to develop - UK took a long time to appear.
In fact, they're oddly static - the number of reviewed restaurants and stores has increased quite slowly for most cities, they haven't done a good job pushing into smaller markets.
Admittedly this is my anecdotal observation but i've been following yelp pretty closely since they launched and honestly up until the Google acquisition attempt, i was wondering if they were short on cash because they seem to spend so little energy on product/design/site and there seemed to be a bit of desperation in the whole 'yelpscam.com' accusations, which appear to be legitimate.
