Not a large number; this is mostly gathered from discussions on internet forums. The sites I hang around on are generally science-fiction related in nature. While there are a few people who know of LW and think it has something valuable, many (relatively high-status) members think of it as being overly "self-important" or "full of hot air"; most don't outright disagree with the overall point (or never pin down their disagreement exactly), but state that the jargon makes LW useless, or that it states obvious things in a pretentious way, or that it's a close-minded community of "true believers" (the places I hang out are largely atheistic, so this is very much an insult).
In some ways, LW has suffered from HPMoR - anyone who doesn't like the story for whatever reason isn't likely to like the site, and I think it's plausible that some of those people would have liked the site if not for the story - though it's also more likely that many more people wouldn't have found LW without HPMoR.
Introducing people to Less Wrong outside the internet, my much more limited experience is that to most people, it's just an interesting blog. It's shiny, but not useful. I've tried to get a family member to read parts of the Sequences in hopes of getting to a point where we could resolve a long-standing disagreement, but they don't show much interest in it.
I've linked LW several times on a (videogame) forum and the reaction has been mostly positive. A few are regular readers now, though I don't believe any participate in discussion. I think two have read most of the sequences. At least one regularly links EY articles on Facebook.
Another small sample, of course. And I haven't really linked articles on FAI/MWI/cryonics.
I've spent so much time in the cogsci literature that I know the LW approach to rationality is basically the mainstream cogsci approach to rationality (plus some extra stuff about, e.g., language), but... do other people not know this? Do people one step removed from LessWrong — say, in the 'atheist' and 'skeptic' communities — not know this? If this is causing credibility problems in our broader community, it'd be relatively easy to show people that Less Wrong is not, in fact, a "fringe" approach to rationality.
For example, here's Oaksford & Chater in the second chapter to the (excellent) new Oxford Handbook of Thinking and Reasoning, the one on normative systems of rationality:
Is it meaningful to attempt to develop a general theory of rationality at all? We might tentatively suggest that it is a prima facie sign of irrationality to believe in alien abduction, or to will a sports team to win in order to increase their chance of victory. But these views or actions might be entirely rational, given suitably nonstandard background beliefs about other alien activity and the general efficacy of psychic powers. Irrationality may, though, be ascribed if there is a clash between a particular belief or behavior and such background assumptions. Thus, a thorough-going physicalist may, perhaps, be accused of irrationality if she simultaneously believes in psychic powers. A theory of rationality cannot, therefore, be viewed as clarifying either what people should believe or how people should act—but it can determine whether beliefs and behaviors are compatible. Similarly, a theory of rational choice cannot determine whether it is rational to smoke or to exercise daily; but it might clarify whether a particular choice is compatible with other beliefs and choices.
From this viewpoint, normative theories can be viewed as clarifying conditions of consistency… Logic can be viewed as studying the notion of consistency over beliefs. Probability… studies consistency over degrees of belief. Rational choice theory studies the consistency of beliefs and values with choices.
They go on to clarify that by probability they mean Bayesian probability theory, and by rational choice theory they mean Bayesian decision theory. You'll get the same account in the textbooks on the cogsci of rationality, e.g. Thinking and Deciding or Rational Choice in an Uncertain World.