Nothing stays free (of ads) forever
Instagram is done experimenting and is ready to ramp up ad revenue. It’s making three big changes today to attract marketing dollars from around the world and other ad mediums. Finally, Instagram will make back the money Facebook spent buying it.
Longer term, I do wonder whether consumers/users ever get tired of the advertising bombardment that is being experienced across social networks. I still don't believe the mythical social-network-that-everyone-pays-for is there (in the near/medium term at least) but whether users will stick with all these networks as they look to make back all the investments in them - it'll be interesting to see what networks walk the tightrope and get the balance right (just look at MySpace as an example of one that got it wrong).