At Balticon, there was a table for humanists, the Ethical Society, and skeptics. I told one of the folks there about Less Wrong-- he seemed interested and I'll check back with him, but he'd never heard of it at all-- it took a little time to disambiguate between Less Wrong and what he heard as a human being named Les Wrong.
Anyway, what do you think of doing outreach to fairly compatible groups (I'd add Unitarians to the list)? And if so, what would be good methods?
Not for groups, but for individual people. When I talk about topics of general interests for rationalists with someone else, I often introduce them to less wrong. I tell them something along the lines of "There's a community of like minded people who likes to discuss similar topics on LessWrong.com".
I think something similar, i.e. organic recommendations can work for larger groups, you just have to use a different format. One idea would be to give a presentation and then add a final slide recommending to check out the website.