User indifference is a much, much greater danger for startups than competitors, big or small. So we advise startups to focus on that. What's going to kill you is the Back button, not Google.
Even if the sub-20k investment doesn't pan out, YC is going to get good press and goodwill out of this. Other YC companies will absorb some of the buzz around any YC success.
The above all increases Rapportive's chance to flip the company even if only under the Greater fool theory.
Consider all the posts made to HN by users mourning the loss of Etherpad, for instance... and look back at them in light of what's happened. Google fashioned the technology into a proof of concept called "Wave," shipped it, started to build a user base, then - oh, look, a bicycle. I wonder if it's one of the new carbon-fiber Cannondales?
Basically, Google has a severe case of corporate ADD, just like any number of organizations who have failed to capitalize on assets they already owned. Believe me, entrepreneurs can eat very well from Google's table scraps.