I joined Mastodon in what I'll call the late beginning: ten days ago.
The total Mastodon and connected userbase was under 100k users. It's at or above 300k now, tripled in less than two weeks. The largest instance, mastodon.social, had 40k users, and was double or more the size of the next largest, mastodon.cloud (which I joined, as the largest open instance). There are now several instances of comparable size, and .social is no longer the largest.
Generalistic and moderated instance.