The definition of "genius" according to American Mensa, is scoring in the top 2% on a standardized intelligence test, such as the SAT, Stanford-Binet, or Wechsler scale tests.

Having only ever attended one Mensa function (Philly Phrolics, quite impersonal), I can't testify either way about the interesting-ness of my fellow Mensans. According to a recent article in my local group's newsletter, the great majority of members (myself included) are virtually inactive. It's like subscribing to a magazine, and never making time to read it. As P.Robst suggests, below, the most "interesting" members are also most likely to have an existing social network beyond Mensa. Hmm.

This problem is offset by the hundreds of Special Interest Groups (SIGs) within Mensa. These various clubs and cliques cover everything from the mundane (needlepoint, sex), to the fringe (UFOlogy, etc.) Most publish periodical newsletters, similar to the local groups. The SIGs are probably a much richer social resource than the local groups, if that's what you're looking for.