Key difference: if you're joining Mensa, you're doing it for the smart people. (Well, that and the signalling, but I think we've established now that the signalling is unlikely to be useful in this case. Or perhaps in any other.)
I would usually avoid going to a restaurant if the food weren't distinctly better than I could make. That wouldn't stop me visiting a friend for dinner just because s/he doesn't cook much better than I do.
The value of mentioning mensa on your CV depends on which country you are in. In India, China and Japan, employers usually consider it a sign of good potential and tend to rate a mensa member higher than a non-mensa member, if other things are similar. In the U.S., I have been told it is not considered that much of a plus and, sometimes even a minus, as a sign of boasting.
Mensa tests, though professionally moderated and standardised, also differ from country to country. In India, for example, they are independent of language and in our tribal mensa pro
It's not a typical OB/LW subject, but Robin correctly pointed out that most rationalists are outside OB/LW, and so I'm asking about one of the organizations that might hold many of them.
A couple of weeks ago I took a supervised IQ test by Mensa due to curiosity and for some CV padding (cheap signaling is a perfectly rational thing to do). Now I got a letter back from them that I'm in top whatever %, and they'd like me to join. I wasn't really planning joining Mensa, or anything else, so I'm wondering - does any of fellow rationalists have any experience with them? Is it worth bothering?
As a bonus here's a quick description of their supervised IQ testing process:
They compute percentile based on both tests separately, and higher of two counts as the result. So you can has 0 points on one (if at all possible), and respectively 148 / 132 on the other, and you're in (2 stddev above mean, or top 2%). The tests obviously check knowledge of obscure English words and meanings and ability to deal with pressure in addition to intelligence as such. Well, I guess no test is perfect.
So Mensa - good or bad?