I'm noticing many problems with your perspective, and since I'm in a good mood this morning I'm going to try and help force-puke the cool aid out of you.
> I seriously admired (and still do) the Diaspora guys for tackling probably the hardest problem there is
Its a trivial problem compared to what SpaceX, Solum, and tons of others are tackling.
> However, how do you go from the ambitious Facebook-Killer to an quickmeme/pinterest mashup
This sentence is a great example of cognitive dissonance. The reality is, it is easy to go from one to the other because they are pretty much the same thing: People get to share stuff with each other on a web interface.
> especially from the godfather YC
> There must be some secret sauce that only pg et al. know
PG invests in dumb shit. YC invests in dumb shit. All the time. Their business model is not "invest in the best ideas in the world" its "invest in people who have the potential to make billion dollar companies".
Furthermore, PG has stated this in his essays, and there is ample evidence in the many startups they have invested in throughout the years.
So, I hope I've helped push you through the social-web-center-of-the-universe and YC-the-creator stage.
I've been there, and its nice to move on.