To the people stating that Instagram is just a way to apply overused filters to mundane photographs: Well, in the hands of boring people, that's what it is.
But to many others, it's a way to share photos and view photo streams from other people that you find interesting. There's a well-constructed social aspect that's missing from other photo filter apps. And for every lame filtered photo of a rusty fire hydrant there are ten truly interesting or beautiful photos. I use Camera+ to tastefully augment my photos then I share them on Instagram, and I have a lot of fun doing it.
I'm not thrilled with today's news but it'll be interesting to see what Facebook does with it.