I love that Instagram has been able to grow and be successful without needing much of a website. While they do have a website it sure doesn't do much beyond sharing a photo. This definitely sends a message that designers, developers, and startups can't ignore. Path is another startup that sets this example. Not too long ago the thought of being a hot tech startup without much of a website was crazy to imagine.
I don't know why Facebook doesn't come up with some image filter of their own. Facebook would easily absorb Instagram's differentiator.