For starters, they're the most arrogant people imaginable, but that isn't the point.
Stupidity comes in all shapes and sizes, and to be truly honest, I suffer from it myself sometimes. These people, whom one could call gifted, are backward thinking, close minded nitwits. Sure they are book smart, but when it comes to the basics of life they can't function. They are socially inept and wrapped up in their own little worlds. Have you ever heard the expression "He's too smart to use a hammer?" Some of these people are like that. Get them out of a high IQ scenario and they are truly incompetent in most things in life. They may excel at math or physics, but opening a jar is a challenge for them. Now, granted, not all of them are like that. Some of them live in the real world like I do, and they get on fine. They are normal people with high functioning minds who excel in many things. I applaud them. The others are adept at bragging up their own intelligence and putting down others who don't share the attribute. They are mostly socially stupid in that they can't interact in the real world without angering and alienating people. They are adept at finishing your sentences for you, pointing out flaws in diction, grammar, or ideas, and are just generally annoying. To be quite frank, I have met mentally challenged people who are better behaved in conversation than some of these people, and the conversations have been of higher quality on occasion.
I like to think that I am not that way. I have the highest IQ in my chapter, and you know what that means... absolutely nothing. It doesn't make me smarter than a car mechanic, or a basket weaver, or a person working at Starbucks. To paraphrase Warpus, everyone excels at something. I'm good at some things, too, I like to think. But it doesn't make me better than anyone else. I am a head injury away from having an IQ of 80. I have worked with the mentally disabled for much of my life. I have compassion for them, I feel for them, and I feel with them. Some of them are better people than these people at Mensa. I think IQ is a useless way to compare intelligence anyway. I'm not smarter than anyone else, I'm just better at puzzles. When you work with the mentally disabled, you realize that IQ is really only a useful measurement to describe intellectual impairment. 90 to 110 is the baseline average for a "normal" person, IIRC. Above that is meaningless, as far as I'm concerned. The people scoring higher are just good at puzzles and taking tests, but that's my own opinion. I will, however, stick with that.
If you are desperate to know how important IQ is as a function of measuring smarts, let me give you a little bit of anecdotal evidence. My IQ is 173. I am, as a result, functionally impaired in the real world. I think too fast, I'm scatterbrained, and I'm always jumping to conclusions, among other things. If you and I start a puzzle, I will be finished before you are. Big deal. I can't fix my own fuse box. I can't do much to my car other than change the oil. I can't for the life of me understand some scientific concepts that I am really interested in (anyone who can explain string theory and Hawking's concept of P-Branes to me wins my undying love and gratitude), and I probably never will. But it doesn't matter. I don't care. I've been reading this thread, and I think that some of you equate IQ to the worth of a person (not overtly, but if you read between the lines...) It isn't so. Everyone is wonderful in their own way. Even the dummies in my Mensa chapter.