I am in a highly organized secret Facebook group mah-self. The thing is that this highly organized quality means that they could jump anywhere if they really wanted to. Perhaps you "semi-organized".
Basically, I think lock-in to any social networking pretty much has to come through a group disorganization, through the fact that a given setup works for some members of the group but these members are not so committed that they'd actually jump from one group to another.
But there are other factors, I think G+ only has traction with early adopters. By starting at Harvard, Facebook itself spread from high-social-prestige people to the rest of us. G+, for whatever reason, may be spreading the same way but that kind of effect only works with the tenuous connections you want to have with people who aren't wholly committed. The cohesive connection you with people in a set group don't require any given medium to happen.
Anyway, personally I'm not going to G+ due it's even-more-draconian-than-Facebook anonymity policy (Facebook's policy is pretty much that they only say they care).
The only thing I see here is the ability to add a nicknames - your "alternate names" - to your "real" name. That is not at all the same thing.
Edit: Comment on the page - "I'm sorry, but the only difference I see here is that you're now listing the nickname field on the hovercard and profile. I see no substantive policy change. Fame was already an obvious and hypocritical exception to the policy; now you're just open about it." That's what I read.
But that's not really a game changer. Whether you are at FB or G+, if you are using pseudo name to protect your identity, than you are rendering yourself useless because you can't be hiding and expect to be networking authentically with the people you know for real. What would make sense for FB/G+ to provide is the ability to have each person choose his/her self-identity based on different situations, i.e, provide complete autonomy to the people on how they wish to portray themselves to the different sets of people. I can be a real name in front of my family and co-workers, but at the same time, projecting and sharing different sets of updates based on who am I sharing with. At the same time, I can be a pseudo name in front of the strangers and/or people I may only know online.
It turns out this is extraordinarily difficult, and if users think they can maintain this separation using a single account, and then they get burned, they are very likely to blame the social network involved. Which is a pretty good reason why the architects at FB or G+ would probably think very, very carefully before implementing such a feature.
I've known a few groups which have survived / persisted across multiple platforms over the years. In one case, migrating first from one hosted forum to another, then self-hosting, then that imploded, a "temporary" forum was constructed (and persisted for years), and finally the original self-hosting platform was resurrected.
Bits of the group survived all of that.
What didn't survive were several members (death trumps all social stickyness), and some political and group-dynamics interactions, including a few fairly spectacular flame-outs. But a core element has survived.
If a group were, as a whole, to decide that FB was no longer where its interests were best served, then a migration elsewhere would be trivial to arrange. Despite my own interest in archives, it's not the depth of social media history that matters so much to most users as the breadth of now. Facebook is where "now" is for most people, though this could change (and has for all prior social network giants of the past: Geocities, Usenet, Orcutt, Xanga, The WELL, ...).
I joined this local car club group, and there's literally hundreds of people every day posting up pictures of their cars asking for... swaps. SWAPS?! This happens in the real world?!
On more investigation there's local groups like "Under $50"... to "Under $1000" - and my gods, they're soooo suspect.
I can understand why they're a big part of people's lives, because they've got a wealth of content!
I think the reason people are not moving off of FB to G+ is because of the groups. These secret/closed groups are heavily organized and ingrained and it is practically impossible for people to make a move to anywhere else. These FB groups are like Yahoogroups (the old fashioned email listserv) which are still going strong as far as I know.