Interesting. In my experience, "nerd" is considerably more pejorative than "geek," connoting social ineptitude in addition to obscure expertise. According to that bastion of cultural authority, Wikipedia (archival, here's a barf bag for you), this appears to be a common debate.
If nothing else, I suppose it's true that only nerds and geeks would argue about the distinctions between nerds and geeks.
Indeed. I view nerds as being the overly intelligent type that lack some social skill. I view geeks as being overly interested in an area of knowledge. You do not have to have a certain intelligence level to be a geek, just a certain amount of knowledge and opinion about an area. Thus not all geeks lack social skills. Since geek does still carry a negative connotation, though, the socially able geeks don't take on the term.
Thus in my example, a nerd could be interested in Star Trek or Star Wars. It takes a geek to go into the discussions of whether the Enterprise or a Star Destroyer would win in a battle.
In another example, the people who are obsessively dedicated to sports and memorize the statistics for various players fit the category of geek (sports geek). Since there are consequences for calling members of the basketball and football teams geeks, the term doesn't normally stick to them. However, the short kid with glasses would be called a geek just for knowing all of that stuff.
I prefer nerd to geek myself. For the nerds shall inherit the earth. The geeks will just continue playing dress-up and arguing if Captain Pickard or Janeway is the better captain.