50M doesn't strike much in FB scale, that's until...
At the time, more than 50 million profiles represented around a third of active North American Facebook users, and nearly a quarter of potential US voters.
Sorry for the crappy formatting, can't edit now, so here's pprint version:
At the time, more than 50 million profiles represented around
a third of active North American Facebook users, and nearly
a quarter of potential US voters.