Heard of Overcoming Bias through the Extropy Institute discussion list, which I've been lurking on for a billion years. (Or a dozen. One of those.)

The main way people in my social circle who were not familiar with LW have become interested in the site is through getting links to specific essays that were of particular interest to them, or of interest to people involved in whichever activity we have in common. (I don't know how many of the HPMoR readers have converted to LW readers, though at least a few.) Just saying "there's this site about rationality and cognitive biases" will get a "yeah, that's cool, whatever" unless the post on the front page is unusually compelling.