Which is to say: network effects are king and people will use what their social contacts already use in essentially all cases. I think that argues strongly against Snapchat as a growth bet, given the numbers in the article.
However, I don't use Snapchat because none of my friends do, I've met some Americans traveling who use it and that is all, I think a lot of people don't even know what Snapchat is while everyone knows what Instagram is even if they don't use it, that is all because of network effects.