Looks like I'm the only one here who actually attended a Landmark event, but I'll say right off I agree with everything else everyone else already said/heard about it.
I do want to add that the reason I went was because there were some concepts I'd heard about from others who did it that felt useful, and I really did find those parts of it useful.
But the initial Landmark training is 3 days, with over a day of just trying to "sell you" on the concept and beat you over the head that you are not successful unless you bring other paying customers. In a class of about 100 people in my class, I think I was one of the only people who refused to identify others who would commit to taking a course. It made them nutty - clearly the Teacher's commission is hurt by not getting 100% of attendees to commit other paying customers. (FWIW they don't spend a solid day trying to sell you - it's throughout the 3 days that they beat you over the head but I calculated it added up to just over a day's worth of commercials and pressure).
I found myself asking a lot - and trying to ask the teacher after which I was never called on again - "If you are so sure this approach works to change lives, why are you spending so much time trying to pressure us into turning other people onto it? Won't we do that automatically if we really believe in it?" I never got an answer.
My overall assessment of the value of that experience: while there are definitely pieces of it that were valuable and useful and I continue to go back to them in my life... overall it's still not worth the expense and the grueling schedule and the bullying into pulling other people into it.