Ok Smartypants.
I just heard about them. The podcast was really interesting.
http://www.smartpassiveincome.com/millionaire-mastermind-groups-jaime-tardy/
Made me wonder what it was like to do it.
I haven't listened to that podcast yet but Pat's talked about the components of a good MM group before.
He recommends a lot of structure: weekly gatherings (in person or via Skype or Hangout), host rotates to a different member each week, limit of five minutes per presentation, each member's specific goals laid out and addressed next week, max meeting time of an hour. It's similar to Y Combinator's Tuesday-evening dinners for their startup entrepreneurs: they have specific goals, they made themselves publicly accountable to the rest of the group, and they know that they'd better have something to show before that next meeting.
There are a lot of mastermind groups among personal-finance bloggers, but they're focusing on the aspects of achieving FI like websites, social media, building an audience, marketing, and so forth. I doubt that anyone is laying out their asset allocation goals or researching SWRs.
Arguably you're in the world's largest (and least organized?) FI mastermind group right here. Or you could form your own chapters like the "groups" on Early-Retirement.org. (I used a group there to collect advice & stories for the book, and then I used it to publish draft chapters for the group's critique.) You could even use the posters in your geographic area for an online or an in-person mastermind group.
One wrinkle would be what a mastermind member does after they reach FI. Do they stay in the group and mentor other members? Do they drop out and disappear to live happily ever after? Or do they just spend all day composing long posts on Internet forums?