I'm having trouble imagining a definition of "important" which excludes a new communication paradigm that connects literally millions of people.

(Whether or not that communication paradigm will ever break a profit is, of course, a separate issue.)

The actual value produced is the marginal improvement it offers over the next best alternative.

In other words, don't compare snapchat to carrier pigeons, compare it to what those people would be using without snapchat: google chat, whatsapp, text messages, email, or one of 1000 other very slightly different ways to chat.

Sure, even a small number multiplied by millions can still become important. But let's not pretend that they invented the printing press.

Another way to look at it is that the internet and mobile data are what's connecting people. The fact that a bunch of people happen to use the same extremely shallow layer on top doesn't mean a whole lot.

Think about technology on the scale of 10 years out, and try and convince yourself that Snapchat will be relevant to human civilization. I certainly can't.

Compare this to technologies that will matter, which are things like mass mobile data coverage, cloud computing, open hardware, distributed data analytics frameworks, low cost gene sequencing, 3D printing, etc.

Popularity does not define importance. Unless we want to add 'Toddlers and Tiaras' and the pet rock to the list of 'important' things.

A sufficiently large pet rock would obviously require some heavy lifting.