I don't really like Facebook, but as has been said already, as long as its integrated in such a way that means you can easily avoid it, then I don't have a problem with it being an option.
I feel like so many of my posts are about wanting Apple to give us more options (see signature

), so it'd be hypocritical of me to just join the Facebook-hating with no good reason.
Having said all that - I do dislike the way Facebook is somewhat insidiously trying to put itself everywhere on the internet, and so if I was being selfish about it I'd rather this wasn't happening, as it will further legitimise and encourage Facebook usage, including all the people who use it without really understanding what they give up for their 'free' service', which I personally think is probably a larger fraction of their users than it should be.
However, I recognise that there are those who both understand everything Facebook does (by which I mean essentially sell its services to users for the mining of their data) and are fine with that, and don't mind it being ever-present in their online world, and would love the kind of integration being mooted here. So for those people, I'm happy, even if for me it'll be an aspect of iOS6 that I'll actively avoid.
P.S.
Whilst we getting these integration options for those who love social media, it would be nice to get some standard options for mobile Safari to block all the social media web 'pollution', such as FbLike, Twitter, G+ buttons on our iOS Devices. That kind of thing might blow the deals Apple have though - and that's a legitimate concern about this stuff too I think. I mean ideally I think it should be a standard option in desktop browsers too, but at least we have plug-ins for that.