I actually disagree; the "Rationality" tagline is highly appropriate, especially as the singularitarians here are devoted to rational thought processes anyway in AI research.
I would, however, like to point out that the site seems to get mixed up with other groups as well:
"RationalWiki" - the highly politically partisan pro-science web page (kind of an opponent to LW, apparently.
Rationalism (philosophy) - Spinoza, Leibniz, Descartes (but they pretty much ignored empiricism so they have little to do with LW thinking)
Rationalism (Ayn Rand) - the worst kind. LW isn't a social-engineering organization, especially one committed to absolute "rational" selfishness.
So the tagline is good, but we should try not to get mixed up with those groups.
"RationalWiki" - the highly politically partisan pro-science web page (kind of an opponent to LW, apparently.
I suspect that one cause is that they get confused for LW and vice versa!
Another might be the Bayes vs. science thing.
Concerning Less Wrong's tagline, consider this plausible reaction of someone looking at LW for the first time:
And here are two real quotes from 2009:
And in reply:
The quoted text speaks for itself really. So therefore I think LW's admins/web designers should seriously consider replacing the rationality tagline with something more savory.