Been thinking more about this, and having seen the demo on video ...
It's slick, really slick. And it will be available for download in 10 days. I predict it will take off. If it does, many will forsake TouchWiz, Sense, etc. But it doesn't stop there. This is a slick, slick integration of an app launcher, newsfeed, messaging system ... For those without Facebook paranoia (and there are many), this is the smartphone OS they have been waiting for. This is disruption.
Home is not just a threat to Google. Apple will have to treat it as such as well. Millions upon millions of iOS users could have Facebook Home envy and some will consider switching. This is, as stated earlier (in this or another thread?), the first real Android-exclusive killer app.
Without being a passionate Facebooker, I still find this quite exciting and look forward to see how every party will respond.