Lots of people used Napster, DC++, email, Usenet, Kazaa, IRC, ICQ, MSN, AIM, RSS, SMS, all kinds of stuff. There are lots of possibilities. Facebook's success is interesting but it's totally possible that something similar could have happened with another protocol than HTML over HTTP, no? Either way, Facebook is basically a commercial success involving network effects, vendor lock-in, good marketing, timing, etc; it's not a technical breakthrough at all.