There have been a lot of misconceptions surrounding the usage of these three words - geek, nerd and dork. In fact they are considered offensive by many people.
Unfortunately, most of them don't even understand the difference between them. Here's a Venn diagram that shows how they relate to each other.
As evident from the Venn diagram, the classification deals with three major criteria - Intelligence, Obsession and Social Ineptitude. One major point to be noticed here is that the usage isn't restricted to education. A person who is obsessed with Cricket and is intelligent with respect to the game of Cricket can be considered as a Geek at Cricket. So the general stereotype of a guy with glasses reading a book for a geek isn't really a great notation.
Terming oneself as a geek/nerd/dork needs a really broad mind. On a whole being termed as a geek or a nerd need not be as offensive as it sounds and people with a really really broad mind might even take it as a compliment.
Coming to myself, I am not sure if I am intelligent, but I am definitely not socially inept. I am considered addicted to Computers and PC Games but not really obsessed, I guess.
I actually stumbled across the Venn diagram when one of my friends buzzed the link at Google Buzz. Do check it out if you would like to read the original article.