Some people think I'm smart (although I vehemently disagree, and will often volunteer evidence to the contrary). Having been at uni for a while has obviously put me amongst (actual) smart people. I have been thinking about what things make someone smart. Recently I have liked the idea that someone's intelligence is purely a measure of their ability to focus on a problem. More recently I have been thinking that in addition to focus (what is 'focus' exactly anyway?) it may also be the amount of distinct chunks you can work with in your mind at the same time. After all, if you can only focus on one single chunk you won't get very far.
I've noticed that smart people often tend to be perfectionists. Perhaps not perfectionistic about everything they do, but certainly with at least a handful of things. For example, I have a friend who is an audiophile. At this very moment he is meticulously sorting and annotating the metadata of his outrageously large music collection. He has a keen interest in sound compression algorithms, and will sometimes even use a lossless algorithm to encode his music with.
Like me, he also is very careful about his spelling and can never knowingly leave a spelling/grammar mistake in a piece of writing, even when it's in short, informal communications like IRC or email. Another friend I made back in first year (who was much smarter than I) put it quite succinctly when he said "I just hate not knowing how to do things" (this was in reference to studying for an exam for a university subject).
I hypothesise that perfectionism is actually a notable factor in intelligence (or, at least, being smart). A perfectionist does not like leaving a job half-done. If something is taught to them that they do not fully understand, their perfectionist tendencies will drive them to try and complete the puzzle -- just for the sake of completeness.
I think this tendency/attitude has its disadvantages though. Firstly there is the possibility of wasting time on useless things (such as correcting a spelling mistake in an instant message sent to a friend who could understand the original message easily anyway).
Also, since a perfectionist has a desire to do a complete, whole-hearted job of a task, there may eventually be less of a desire to take on certain large tasks. That is, there is an attitude of "I don't even want to start this project because I know that once I've started it will take a lot (possibly an indeterminable amount) of time to finish it to the standard I would like". Finishing it to a lesser standard is not an option! I have found this happen in a few projects I've needed to do, and I see some of my friends suffer under it too. I think this is at least part of the attitude of procrastination rampant among uni students and postgrad students in particular.
Sometimes the scenario works out to be that the only way to stop the project from taking over your life for months is to do no work on it until the deadline is in two weeks. Then the project has only occupied two weeks of your time, and the excuse that you weren't able to do it to the best of your ability is due to 'external factors' outside your control (namely the deadline).
Finally, I think it can also lead to being overworked, leaving the perfectionist burnt-out and unmotivated. This could possibly spell the end of a person's perfectionist attitude in that particular area (such as studying at university).
Perfectionism isn't like Force-sensitivity -- it comes in varying degrees. Perhaps being *really* smart is knowing when to perfecct something further or when to just let it go.