I'm dissatisfied with the traditional definitions of these terms. Heck, Wikipedia wants to merge the two entries... The way I see it, A nerd is someone who has a bunch of specialized knowledge by virtue of concerted effort and study, generally formal education in a particular field. A geek is someone who has similar knowledge, but has gained it out of sheer desire to attain that knowledge, perhaps on the job or through experience. Nerdiness pays the bills; geekiness is what you do for fun. Cliff Clavin is a classic extreme geek in my book, although he often wanders into the world of triviality.
So I'm a nerd about records management and Chicago history, but I am a geek about airplanes, computers, and trains. Ok, elements of my computer knowledge border on nerd-dom, but only in a few small areas.
Funny thing is that I periodically call upon my geekiness to help out my nerdiness. So why do I keep some things classified as "geeky" -- particularly the computer stuff? Well, the way I see it, I know a lot about computers for a records manager and I have some particular areas of knowledge that will spin an IT manager's head around. But when you run up against people who really know computers, you're just a minor geek against their nerdiness. That happens with a fair amount of regularity when talking to two members of my staff. These guys are hardcore. A couple months ago, I showed one of them my home network layout. He then showed me his home network. He runs a series of virtual machines. He has built in hardware firewalls. He has various filters running to keep the bad stuff out. I simply trust Symantec and Linksys. My other staff member will periodically walk me through the finer points of forensic analysis, root kits, and hackerdom. I smile, nod, and play sponge -- there's geekiness to be learned here!
At the end of the day, I have to assimilate all that stuff, apply good judgment to the decisions that I have to make, and hope that I'm properly translating all this stuff to the lawyers. Oh yeah, there's another set of geekiness in my world....