I don't think there's any big A2K discussion group over at FB. There are people who are A2k members who are also FB members, and some of them are friends on FB. I am FB friends with some Abuzz/A2k people. I'm fairly sure I'm not in the A2k group on FB. I know there are some smallish groups that seem to consist primarily of former Abuzz posters that discuss topics of particular interest (cooking/gardening/writing ... that sort of thing)
Most people use their real names on FB, some use their A2k names, others use other names entirely. Most of them can be recognized by their posting style.
It's been entertaining to find real-life/A2k overlaps that I hadn't known about til discovering A2kers are mutual friends with real-life friends/acquaintances.
There's a lot more real life going on at FB. Not as much mmmmm fussing and feuding over hypothetical crap.