Read and weep.
“So all things considered, MySpace has cost Murdoch’s empire something like $1.3 billion.”
No doubt a tiny dent in News Corp armor.
This might happen to Facebook too, yet less likely.
It will much more likely happen to the rather redundant (and increasingly many) location services, like Foursquare, Gowalla, Brightkite etc. There are so many players fighting for the user base, that have arguable or no business models, and they are easily replaced by services that encompass other things, like Facebook and Groupon.
Not that I see any slowing down of introductions of new services. Rather the opposite, and they are all more and more basic/simple, due to the possibilities of interlinking services via public APIs. Hence, the opportunity landscape is still open, but the risk of financial failure increases.