In the worst case, you'll fail to scale due to technical shortcomings like Friendster and become forgotten while later entrants like Facebook eat your lunch.

There was a time when "being web scale" was a real concern. That's why big companies like Google make such a big deal about it in their technical interviews. Now most of the hard work has been done and exposed as services so today's engineers have it easy. Even an untrained teenager can stand up a web-scale service.