We'll see how my s.o. reacts to it, but on my machine it does absolutely nothing.
In case you're wondering what is in my hosts file:
127.0.0.1 www.facebook.com
127.0.0.1 facebook.com
127.0.0.1 connect.facebook.net
127.0.0.1 facebook.net
127.0.0.1 fbcdn.net
127.0.0.1 www.fbcdn.net
0.0.0.0 badge.facebook.com
0.0.0.0 blog.facebook.com
0.0.0.0 en-gb.facebook.com
0.0.0.0 developers.facebook.com
0.0.0.0 touch.facebook.com
0.0.0.0 de-de.facebook.com
0.0.0.0 stories.facebook.com
0.0.0.0 it-it.facebook.com
0.0.0.0 hu-hu.facebook.com
0.0.0.0 peace.facebook.com
0.0.0.0 et-ee.facebook.com
0.0.0.0 az-az.facebook.com
0.0.0.0 0.facebook.com
0.0.0.0 apps.facebook.com
A nice side-effect of this seems to be that the web has become a lot more responsive. No more 'like' buttons popping up all over the place.edit: regarding my s.o. it's been an interesting morning, this app seems to have opened her eyes to facebook in a different way. No more apps.