I've been a long time user, and critic, of Google+. Now I'm helping those who want to move off it to find new homes, which has been interesting in itself.

I'd previously measured active public G+ posting activity, by way of the site's own Sitemap files. Stone Temple Consulting expanded those methods to show that:

* 91% of all G+ profiles (2.2 billion at the time) had never posted publicly.

* About 5% (110 million) profiles showed some public posting activity, other than YouTube (a factor that had inflated apparent activity markedly).

* About 6.5 million profiles (0.3%) had over 50 posts ever.

* About 3.5 million profiles (0.16%) had over 50 posts and activity within the previous 30 days.

That from March of 2015, based on a very large sample of 500,000 randomly selected profiles, using methods I'd developed a few months earlier.

More recently I've been looking at G+ communities, on which there'd been virtually no quantifiable information. There are over 8 million of these, though the vast majority have few members and little activity: the 45%ile membership is 1, the mode is 2, the mean around 130, itself far above the 95%ile (118.5).

There are 66 communities of 1 million or more members, 1,100 > 100k, 10,044 > 10k, 64,775 > 1k, and 390,390 > 100. I've found vital communities across these size ranges, with over 100,000 having 100+ members and activity within seven days prior to accessing, over January 5-6, 2019.

Bigger isn't necessarily better. Looking at interactions (posts, comments, plus-ones, shares) by community, size matters little. It's the posting activity that drives other engagement, and the per-member engagement tends to peak between about 100 and 3,000 members.

Many of those communities are looking to move elsewhere, as are other G+ users and less formal social or other groups. Among the frustrations Google has thrown at them, the two leading official Google+ Community-focused communities, Google+ Moderators and Google+ Aspire, were shut down by Google before most communities had really started addressing migration. In the case of the first, Google shut down the community for six weeks without any notice, with users posts sitting in limbo "held for review", but appearing as if they'd been posted by the author. In the second case, an 80,000 member community focused on Community leaders was shut down without any prior notice.

There are several places Plussers can go for information and coordination.

The Google+ Mass Migration community, over 4,000 members since 8 October 2018, is the central discussion point on the site itself:
https://plus.google.com/communities/112164273001338979772/

There are numerous off-G+ rallying points, with the /r/plexodus on Reddit specifically aimed at the migration process itself:
https://old.reddit.com/r/plexodus

And there's a Wiki with extensive information, including FAQs, planning guides, platform comparisons, data migration information, and directories of users, communities, and off-G+ meeting points, and more. Much a work in progress, but again, useful to those migrating off the platform:
https://social.antefriguserat.de

Links to many other communities, sites, and resources are included at all the above.

I'm finding the process and prospect of moving some ... not entirely clear number of users ... off a dying platform and onto new homes a hugely interesting prospect. There's an opportunity to break out of the surveillance capitalism disinformation monopolist mold, and also risks. I've found out a tremendous amount about developments over the past 5-10 years in online, social, and user-generated media, been digging back through history, discovering I'm in close contact with some very knowledgeable people (a key Project Xanadu member has been in my Google circles for years, I've just learnt), and more.

And there's a lot we're sorting out about what a migration process entails and requires, and the distinctions between succesful migrations and failures. I see this being useful to others in the future, possibly sooner than we might expect.

Interesting times.