A lot of us spend a fair amount of time labeling people and lumping them into categories, possibly for our own mental convenience in thinking about them, and possibly because of that delightfully smug sense of superiority you get when you think you have someone figured out. With that in mind, I'd like to take a stab at fleshing out some of the labels used to sum up personality traits I share. Specifically, "nerd", "geek", and "dork."
These words have gone through a variety of overlapping meanings, "nerd" was a word invented by Dr Seuss for a fanciful animal that gradually took on its current meaning through slang, a "geek" was originally a performer who bit the heads off chickens, and the word "dork" came about as a semi-censored derivative of Richard. You may use these terms in very different senses than I do, but I'd like to set up some distinct definitions I find useful. In short, I think of nerdiness as an obsessive singular interest in a subject, geekiness as an interest in topics outside the mainstream, and dorkiness as being characterized by social awkwardness or lack of relational expertise. You can be all three, or any one of the three and not the others. But let's tackle each in a little more depth.
I prefer to consider "nerdiness" and possessing obsessive interests separate from the other categories because I think it applies to so many fields. My little brother is very much a music nerd, he does a lot of research on songwriting and learning about talented musicians, he's overflowing with information about the stuff he likes, and when he gets into something he pursues it with a passionate single-minded nerdy zeal. I'd consider someone who cares about the minutia of philosophy to be a philosophy nerd--a nerdy interest is something you pursue far past the point to which most people take it, and a nerd is someone who's characterized by that kind of single-minded devotion. It can be in relation to a mainstream topic or an obscure one, whether you prefer fussing over cars or 8-track tapes. And it's probably the most socially acceptable out of the three traits by itself, it takes a certain amount of focus to get ahead in a particular field, although when taken to an extreme you have someone who only cares about their one particular topic.
I prefer to think of geekiness as an interest in topics outside the mainstream. Whereas nerdiness to me carries some connotations of expertise or brains, a geek could just be someone who enjoys video games, science fiction, math, or computers more than the average individual. The frontiers of geekiness are fairly elusive, yesterday's geek is tomorrow's everyman. Three quarters of heads of households play video games, and almost everyone uses the internet and social networking sites like facebook. What were once fairly exclusive hobbyist niches have become more and more mainstream. Geekiness can mean being on the cutting edge of technology, or just someone who pursues obscure stuff before it becomes popular. Lord of the Rings, Batman, and Star Wars are fairly mainstream, they've made a pretty big impact on the larger culture to where people would know what you're talking about if you reference them. Terry Pratchett, Sandman, and Firefly are a little less so.
The main distinction I want to make between nerdiness and geekiness is that I think of nerdiness as being related to expertise in a particular area, and geekiness as simply having interests that fall into the niche of a particular geek culture that's outside the mainstream. You can be a nerd about understanding fitness, and you could be a geek about obscure music. A nerdy geek would be someone who takes their obscure interests and strives to master them and achieve a level of proficiency. Nerds go to college and study obsessively, and geeks buy comic-books and play video games. It's possible to be both, or neither.
The last word in my personal classification is the most derogatory and the one that has the least chance of ever being reclaimed by the nerd community at large. I think of a dork as being someone who's simply socially awkward, slow to pick up on social cues, or generally shy/antisocial. As you may have noticed, all these traits are related: someone who's socially awkward may develop obscure interests since his interests aren't based around what his peers are into, and may be more inclined to focus obsessively on studying a particular subject; someone who's gifted in their ability to focus and study may find more obscure topics more rewarding and have less interest in socializing; and someone who's interests are obscure may find they have less in common to talk with people about, and more of a reason to narrow themselves in on a particular area.
As someone who's been various flavors of shy and awkward over my life, being sociable wasn't something that came naturally without practice, which I suppose is how most people relate to Math. It takes a certain mental leap of realizing that it's as possible for you as anyone, and overcoming your fears of things not turning out well. Whereas Math is about understanding explicit logical rules, socializing involves learning all kinds of implicit and subtle communication involving body language, tone, texture, timing, and understanding all the things people don't communicate directly. Dorkiness to me is a lack of being versed in social norms and not being as skilled at adapting to different social situations. Someone dorky could know they have difficulty fitting in and act shy to compensate, or not be aware that they have a problem and make other people uncomfortable to be around them. Or they might claim to find small talk and socializing less interesting than their own interests. And this is where most of the stigma associated with the trio of traits comes from. People with obscure interests or a passion for a particular subject are often assumed to be outside the social mainstream as well.
In some ways there's a certain tragedy to all this, I've seen a lot of nerdy/geeky people try to strongly disassociate themselves from dork stereotypes or pick on people who are socially awkward to make it clear that they're not like that. Some people can even be self-conscious about admitting to liking something fairly obscure or indulging a nerdy interest in a particular area. I'm aware of far more nerds who've helped people out with their math homework than nerds who've been offered help for all the things they lack expertise in.
I find a nerdy passion for anything to be more interesting and engaging than simple apathy, even if it can be taken to extremes. Focusing on topics few other people are interested in can be isolating, but it's because people are willing to try stuff out that isn't mainstream yet that people get exposed to anything new. I see my own nerdy obsessions as a dangerous yet powerful force for good or evil, my geeky traits as a personal stamp of pride in my culture and all it brings the world, and my dorky traits as a reason to keep in mind that other people are actually worth it, and it's worthwhile to pursue social ends as well as intellectual ones.
To sum this all up in a bit of self-reference: Writing a blog post analyzing types of people? Nerdy. Writing it about a particular subculture? Geeky. Not being able to get anyone to read it? That would be dorky, but I'll hold out hope.
Update: One thing I've realized since writing this and discussing it with people is that while nerdiness is an absolute scale of obsession, both geekiness and dorkiness are relative to a particular culture. Being into French cinema may be perfectly normal if you live in France, but it would be a little geeky and obscure for someone in America, it's outside mainstream cultural taste. And while some elements of dorkiness are fairly universal in being able to relate to people and communicate well, a large component of dorkiness is how well you're adapted to a particular culture's norms. You may get by fine in America or even an english-speaking country where you're familiar with all the customs, but if you get plopped into a country where you don't know the language as well or understand how people typically interact, you'd be a hopeless dork in that context. And some subcultures can even create their own system of social expectations and interactions, that could leave normal people feeling out of the loop socially. Some people certainly don't put in the effort to adapt socially to their contexts, so there is still an absolute component of how much effort you put into connecting with people, but a large part of how dorkiness comes off is relative to the environment you're trying to fit in with.