We tried it, disliked it as a whole, and dropped it while retaining those ideas we found useful.
But then, we're a small company, with an already (nearly) flat structure, and already built around largely self-determining teams. So what Holacracy offered above what we already had was rigid structure, and cumbersome terminology.
It also has a weird religious vibe in that the Holacracy franchise holders who we turned to for input on our implementation of it refused to work with us unless we adhered to the defined process 100%. No modifying it to suit our company.
The formal governance meeting process caused a severe backlash when rigidly adhered to because it only allowed one "reaction round"[1], so if someone else's reaction caused a new viewpoint to arise in your mind, but you had already spoken, too bad. Our facilitator who had attended the training rigidly enforced this process, and several people, myself included, felt silenced.
So yeah, as we weren't a traditionally pyramid structured company to begin with, we had very little to gain from it - we tried it because we had started with 5 employees and no governance beyond "let's ask the boss", and we had grown to a point where we needed to get _some_ governance in place, because while intra-team decisions were fine and dandy, how we made decisions affecting everyone was really unclear.
So in the end, we dropped it. We have kept some of the ideas we found useful, for example the separation between governance and tactical meetings, and the idea of the 'lead link' or their equivalent being opposed by the 'rep link' equivalent, in our case, it's our proxy product owners (PPO) and their eternal opponents are our scrum masters. It's a healthy tension between what the business wants and what the team wants.
The other valuable thing we've kept was the objection and objection testing process - if someone has an idea, objecting just because you don't like it is not considered valid. You need to be able to present a coherent argument as to how the proposal, if adopted, would harm the company. It means that the "Bah humbug" curmudgeons can't stall innovation. Basically it boils down to "Would it hurt us to try this?" as a test for a new idea.
So now our governance consists of a small group of 'executives' for want of a better word, and what we call "The General Circle". The "executives" is our boss and two 2ICs (to increase our bus factor to keep our business team happy) one with an HR and finance focus, the other with a businss analysis / product development focus. This group's primary focus is the relationship with our business team, but it also handles the aspects of running a company that require handling an employee's confidential information, like pay reviews and HR issues.
But every other cross-company decision is made by the General Circle, a group consisting of the PPO and scrum master from each team, plus our finance and HR specialists. These discussions are totally open to anyone else who wants to attend, and our financial performance is tabled as a matter of course, with more detailed numbers and budgets available for the curious. PPOs are theoretically appointed by the General Circle (our existing PPOs were in their roles before this governance guff, so no new ones have needed to be appointed yet), while Scrum Masters are selected by the team however they like. I think all our teams rotate it every six months or so.
Oh, and we also like the election process from Holacracy - write down a person's name on a piece of paper, with your name on it, and then in the discussion, you say why. After everyone has explained their reasoning, people can then change their votes if they heard a good point that persuaded them.
[1] http://holacracy.org/how-it-works
Has anybody operated under Holacracy and speak to it?