Geek Yes Yes Yes
Nerd Yes Either Yes Science
Dork No Either/No Either/pop

Social skills:

Geek Yes
Nerd No
Dork No

Here’s how I break it down (pretty close to Andrew, but I would switch geeks and nerds). I get this from my friends and I who are all either geeks, nerds, or dorks and will be insulted if you call us the wrong one. :)
Geeks: very smart, often into technology, have their own sense of style~which is not cool by the poplular kid’s definitions, but they do know how to dress. Often wear glasses as well(and pull them off quite nicely). have quirky, offbeat personalities, but they do have personalities, and do have the ability to communicate and socialize with others who are not geeks (even if they often choose not to).
*Note: this might be a little biased, seeing as I do have a bit of a thing for geeks.*
Nerds: this is the next category down. also smart, but usually the most apt in areas of their own interest and don’t care to waste their time sharing their insights with the rest of us who don’t spend our every waking hour alone in our rooms studying it. also often wear glasses but do not pull them off the way geeks do. do not have fashion sense or social ability.
Dorks: the bottom of this totem pole. they are not even smart. they are stupid, clumsy, no fashion sense, very little social ability, and often smell bad/do not have good personal hygiene.

*Side note: a person from any of the above three categories may be overly into Star Wars, Star Trek, Sci-Fi, Video Games, D&D or whatever, but it doesn’t specifically peg them into one of the categories. These are things that geeks, nerds, and dorks potentially could all enjoy (although dorks may have a hard time understanding).

@ Amanda H: I couldnt agree with you more.

(I was actually an athlete. Sorry.)

Squid was a very popular put down when I was growing up.

My husband, however, is very picky about the distinction and swears that he is not a gaming nerd, but a gaming geek.