One of the primary problems with the rationalists, humanists, atheist, skeptics, etc. is that there is no higher level organization and thus we tend to accomplish very little compared to most other organizations. I fully support efforts to fix this problem.
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?