Really, and it's not going to be "completely" separate anyway. All that means is that Facebook currently plans to keep the business as a separate unit and the software as something that won't be integrated into Facebook directly. But otherwise it's going to be as separate as YouTube is from Google, which is to say less and less.
So, for now you can post Instagram to twitter and elsewhere, but at some point I'm pretty sure that will get shut down, or at least you'll have to post through Facebook somehow.
Yeah I agree with what you're saying. It'll be interesting to see how it pans out.
Also how much is Twitter worth? Could Apple buy it?