I was amused by what people have been saying, especially the little side-debate about engineering vs. physics vs. mathematics. I am a professional mathematician. I don't have any stats like IQ or whatnot to boast about, but it is fair to say that I am better at analytical thinking than the average person.
I can't say I can speak for all my peers, but I think most of my peers (in professional academics, cutting-edge scientific/mathematical research, etc) would probably share some of the same views as me. So here are some thoughts I have about how I deal with people who are purportedly "more normal" or "less intelligent" than me:
1. Intelligent people can still have exactly the same interests as people who are supposedly "less intelligent". I talk to my friends (who are all researchers) about sports, especially track, as well as popular music, movies, etc. I really don't think there's anything that normal people like that very intelligent people can't like.
2. Literature is one of the most notable interests that normal people don't find as interesting, but which is of interest to a wide variety of intellectuals (as opposed to, say, physics, which is really only of interest to a very small subset of the population). I don't mean reading fiction - I think everybody is capable of enjoying that. But there are some forms of literature that are simply too abstract (20th century philosophy, for example) for the average person to enjoy. This is occasionally a downer for me. It's not that a "less intelligent" person can't appreciate these things, but I think it is certainly harder for very technical literature to be accessible. Occasionally I'll forget that this is the case, and when I bring it up during a party or something, nobody will be interested, so I drop it.
3. It is difficult to relate to how other people reason out something that requires weighing several factors. That doesn't mean that others are doing something wrong, but simply put, I have a completely different way of approaching most problems in life. The most basic example is financial problems. I'll admit that I can perform pretty large computations in my head. It's usually not a very useful skill, but it allows one to really quickly estimate quantities like "how much will it cost to do X?" When I discuss money issues with people, usually there'll be some problem that comes up that has a solution that seems very clear to me, but often it's simply because I run a bunch of numbers through my head very fast.
A mathematician is trained to work in generalities - to solve a whole range of problems by reducing everything down to a single problem that you can solve abstractly, and then "plugging in numbers" and whatever other specific conditions are needed in order to solve some specific problem. Most people work in the opposite way. They solve a lot of problems specifically, then build up some general experience or intuition about how to solve it, so that when they are faced with a similar problem but in a slightly different scenario, they have an idea of what approach to try.
4. It is frustrating to have arguments with people who aren't trained to make completely logical statements. That doesn't mean that I'm completely logical either - I definitely say stupid things or, in the heat of a debate, make a claim that I can't back up whatsoever. But the ubiquity with which people make arguments that do not obey the rules of logic can sometimes be very frustrating. Usually such problems stem from confusion over what directions logical implications go in. A basic example is if I write numbers on the back of my hand and on my palm. I tell you that if I have an even number number on my palm, then the back of my hand has an even number. I then show you that the back of my hand has an even number. Many people will incorrect deduce that my palm must also have an even number. Furthermore, if I show you that the back of my hand has an odd number, most people will not deduce that my palm must also have an odd number.
5. Memory - sometimes it's tough to talk to people who don't remember as much without putting extra effort into it. I know memorization isn't considered to be a part of intelligence, but I think it's worth discussing anyways. There are a lot of examples of little things where I have to do something a little bit unnatural in order to fit in with some people.
For example, sometimes I'll continue a conversation with somebody later, but I'll find that that person doesn't actually remember much of that conversation, whereas I will have remembered every last word spoken by both parties.
Or, I might go up to one of my runner friends and say "Remember that race in 2008 when person X ran a 4:06.23 mile and ran splits A B C D?" and usually my friends will just say "no", even if they were present at the race. I have to remind myself that usually people don't remember information in that way.
Another example is if I'm discussing a song or a movie with somebody, and they mis-remember a particular bit of dialogue or don't hum the right sequence of notes exactly. There's no reason why I should correct that person, but in my mind I have to stop myself from thinking, "Why can't he/she just do it the right way?"
So all these things may seem so petty, and they really are. I'm not constantly thinking ridiculous things like "Why is he so stupid?" or whatnot, but it's rather that my whole way of recalling and processing information is so different from many that it is hard to coordinate with people when such information is to be shared.