I'll post here what I did over on reddit:
I go all the way back to 1975 with Werner and his minions. Like the CoS, Landmark got into the "life-coaching" racket in the '90s, but it seems to me that it was one of the very earliest human potential cults to identify and pursue the "corporate culture change" market in the 1970s. I was sufficiently "taken" with est back then to try to introduce it to several corporate and governmental organizations in the LA area at that time. I found out quickly that, while Werner (aka Jack Rosenberg) himself "had a plan," his subordinates really didn't "get it" (yet). And I walked away from what would have been bad karma for my own credibility at the time.
Since then, however, est evolved into The Forum, the Landmark Forum, Landmark Education and Landmark Worldwide. By the '90s, anyway, they had wormed their way into several of the major IT concerns in the Bay Area, including (so it appears) Apple, Hewlett Packard, Oracle, Qualcomm and eBay, that I know of. Landmark's presence was facilitated by very high-level contacts in those companies who had come under Werner's et al's spell via the "basic training" and subsequent programs.
For anyone familiar with the est / Landmark lexicon and patois, it's pretty easy to tell when senior managers have drank the Kool Aid. Disenchantment soon followed, however. One notable female executive who turned "powerful" starred in a drama that shredded one of the biggest computer manufacturers of the '90s and early '00s, and rumors flew among the illuminati. While Landmark continues to have residual (and sometimes direct) influence upon the (mis?-) management of some of the firms in the SV, it's no longer the hot ticket it was at that time.
That said, the residual influence via the rather cynical use of the sort of techniques described right here
in several, currently quite significant (and very fast-growing, hint, hint) corporations appears to continue. One familiar with the patois need only watch a few Ted Talks (a hot mess in itself now) to see who's bought into the "sky's the limit" belief system well described in C. L. Mithers' very discomfiting book about The Center for Feeling Therapy, a deal that bought into hyper-narcissistic est-ism in about '73 or so. (While est was never a "classic" MLM, it certainly utilized the work-yourself-to-death-on-the-way-to-the-promised-land-(not) interpersonal manipulations typical of such deals.)
With respect to ICF in particular, I can only say that while the number of ICF-credentialed LCs does seem to rival the hidden credentialling of LCs by the CoS (in Hollywood), the levels of sophistication -- and market penetration -- do not not seem to be what they are among the latter group (which isn't real "sophisticated," either, actually). Frankly, if one is really egregiously ruthless about fast-tracking a bullet train to corporate success in this manner, they'd be better off to find some of rats who jumped ship from Amway and Herbalife.