Just to further derail this topic...
I like instagram. Sure people could post them to Facebook, but it's kind of enjoyable to go there knowing your only going to see photos. Also, people seem to take more photos if they have it than they otherwise would have with just Facebook.
What they need to improve on is the ability to zoom in on pictures in the app.
The great thing about it is if you don't want it, you don't have to have it.