Informed techies are a powerful force. Look what we did with Firefox: we recommended it to everyone and it worked. We are asked which antivirus to use. We are asked how to do X or if we know of a program to do Y. When we speak, the mainstream eventually follows.

That is true, the network effects make it a more complicated equation though, using Firefox didn't mean that you can no longer use certain aspects of the web. I guess it has to do with a critical mass of people, first enough trying your product that it's visible that facebook is no longer the one stop shop for all your friends data (I guess this is what Twitter is, although it's not so much a general purpose social network). Then eventually you need to get to the point where enough users are on board to make it a better use of a persons time to communicate through the new network without losing to much value.

Once you hit this point there is no coming back as has been shown with myspace. I guess a parallel could be drawn with IE - FF there, once a user has been converted to FF and decide it is better IE faces a monumental task to get them back, something they may never achieve, always appearing to be one step behind with a heap of non standards syntax for good measure.