I told an intelligent, well-educated friend about Less Wrong, so she googled, and got "Less Wrong is an online community for people who want to apply the discovery of biases like the conjunction fallacy, the affect heuristic, and scope insensitivity in order to fix their own thinking." and gave up immediately because she'd never heard of the biases.
While hers might not be the best possible attitude, I can't see that we win anything by driving people away with obscure language.
Possible improved introduction: "Less Wrong is a community for people who would like to think more clearly in order to improve their own and other people's lives, and to make major disasters less likely."
Fixing the description to not require a lot of background information won't help if you don't fix the content to also not require a lot of background information.
And honestly I'm not sure the site is right for somebody without a lot of background information. Some of the material here is way too persuasive without giving any implication of the existence of counterarguments or criticisms - for example, anytime Eliezer mentions the Stanford Prison Experiment anywhere. And the reinforcement system here encourages groupthink of the ugliest sort. (I am manipulative and rude fighting positions Less Wrong generally agrees with? Downvotes, naturally. I am manipulative and rude fighting positions Less Wrong disapproves of? Upvotes!)
There's a minimum level of information and curiosity necessary to make Less Wrong a constructive experience. Otherwise it's going to indoctrinate rather than inform. Don't change the barriers to entry without giving what people are entering a good hard look; the barrier should match the building.
People below that level are unlikely to find LW appealing. They might poke their nose in, but they'll leave quickly.