Foursquare and exponential adoption

Is anyone besides me noticing that each successive social networking craze gets exponentially faster adoption?  Myspace to Facebook to Twitter to FourSquare - each time we get twice the adoption in half the time.

This is one of many symptoms that tell me that I am living in the time of the singularity.  The feeling of acceleration is palpable, as the Wired -> Tired lag time gets shorter and shorter.  Is this how it feels to drop into a black hole?

Not that I'm complaining.