We've all heard similar propositions, but at least this request is written by an eloquent persuader who clearly has ambition; it includes social proof and trust factors.
Unfortunately naivety is something everybody has to work through.
3 years ago, I received a very similar e-mail to this on the grad student mailing list at my university. I was naive enough to respond.
I spent a year neglecting my PhD and churning out code for this "startup" while the founders moved gradually further away from the idea of a social network and towards something akin to the million dollar home page. When I eventually quit, they couldn't find anybody naive enough to replace me and none of the other three guys (2 marketing, 1 graphic design) knew the first thing about programming, so the whole thing imploded.
I learned some good lessons from the experience, though.
Don't see social proof or trust factors to be honest.
The reddest flag - "We expect 95% of college students will be active users within 4-8 months." And no insight into how they feel they can do this. Claiming market share of any kind is always tough. In 4-8 months, even more dubious.
Unfortunately naivety is something everybody has to work through.