No wonder. Anecdotal of course, but I see my friends spending more time on instagram and people on the train or bus browsing instagram. I don't remember seeing FB on someone's mobile in the last 6 months.

It will only grow bigger and at some point when it becomes too big, you see less friends posts and more advts and people move on to something else. But for next 2 years, Instagram's going to be Yuuuge.(Huge)