I've decided my wife is a geek. I am a nerd. The two aren't mutually exclusive, but they are different skillsets that may or may not compliment each other, depending on the problem at hand.
Nerds (as one, I feel confident in the following):
Hoarde useless knowledge: For example, I know how to make flint tools and have done so. I know how to field-strip most guns, and own none. I can identify and match most aquatic insect hatches while fly fishing and carry a kit to tie at the waterside. I have memorized all dialogue to all Monty Python movies. I know how many inches of sand it takes to filter organic contaminants from water. I have read all of HP Lovecraft despite the prose and can remember all the Mythos entities. I can bake, but never use recipes. I can identify almost any syndicated TV quote - ditto movies. I have the fashion sense of a small armadillo.
Geeks (Guessing here, based on observation):
Scatter potentially useful knowledge: My wife can explain how to use Red Hat and I never know what she's saying. She can use every keyboard shortcut there is and laughs when you don't know them. She wonders why everyone doesn't have a database and tries to explaain why Excel doesn't count. She veers off in Future Shop muttering "Oooo, shiny" and then tells me why the thing she's looking at is good, then spots something better. She isn't sure what Gilligan's Island was about, other than there was a boat. Discussions of bands she's never heard of bore her. If something either fails to blow up or cry quickly in a movie, she wanders off.
We nerds seem to cling to the anal-retentive edges of Aspergerville, while the geeks scurry around the suburbs of A.D.D. town. They spend their time discussing tech and wondering what is taking those nerds so long with that flint spearpoint that you can't upgrade the firmware on, anyway.