One of my professors disapproves of using the word when children are nearby- adults may know it's not a bad thing, but children won't, and will fear being called those mean names if they show an interest in their schoolwork. I've heard others argue that nerd should remain an insult; that identity is all they had when they were younger, and it's infuriating when pretty girls or cool boys try to take that identity from them, wearing retro Nintendo t-shirts without knowing what it is to be picked on and excluded.
My initial problem with the word still stands- what the hell does it mean? Does it mean virginal scientists? Married Star Trek fans? Mensa members? Straight-A students? Boys who like Halo? Girls who like Harry Potter? Social rejects? Cute kids with glasses? Do you have to complete a long checklist that includes all of the above and more, or is it just a state of mind?
Labeling shouldn't be important, but all too often it is. Humans like forming tribes, and we like having ways to distinguish ourselves from others (or the other way around.) Expanding a label risks making it meaningless, and limiting it may mean kicking out people who "deserve" it just as much as we do (and is ultimately unenforceable in a court of law.) Given the unique range of characteristics in any given person, labels are generally incomplete to describe them (that Star Trek fan may have been a star football player in high school- does he still count as a nerd?) Labels can be insults applied to people we dislike, or they can be impossible standards we try to measure up to. (Jillian Venters, Headmistress of Gothic Charm School, has written about the folly of defining "how goth you are" by how you measure up to others.)
So what the hell is a nerd? I didn't know in first grade and I don't know now. I still use the word at times, but I've become much less confident about it. And I have learned, at the least, to be mindful of the company in which I say it.