If Facebook can grow to 750m users this quickly isn't it safe to say the infrastructure/adoption exists for another company to grow to that number even faster?

If Facebook can grow to 750m users this quickly isn't it safe to say the infrastructure/adoption exists for another company to grow to that number even faster? Let's stop pretending it's the 80's and only one company can figure out how to rule a market (Microsoft). Facebook, too, shall pass. We of the technology world should know this better than anyone.