Alright there seems to be some confusion over these three terms and most people (especially those that poke fun) tend to interchange them! But there are slight differences in each...of course, that does not mean one can't crossover into another term...(example a nerdy, geek)
A nerd is usually someone who is extremely smart, or a bookworm. They usually know a lot about a specific subject such as mathematics, the sciences, or chess. They are usually very logical and their decisions are very calculated.
A dork is someone who is socially unacceptable. They dress wrong for the occasion, they wear 2 different pairs of socks, their clothes don't match, and they may smell. They are just socially inept, in every possible way.
A geek is someone who loves a certain hobby (usually out of the ordinary) and is very knowledgeable about it. Hobbies such as Science Fiction (more specifically Star Wars or Star Trek), Fantasy (a.k.a. Lord of the Rings), computer programming/graphics, or loves comic books.
Now, I'm a geek! And proud!
What are you?