Every time I think I have nailed the "nerd mentality" something crops up to make me reconsider my position. It's almost as if nerds are like regular people who don't follow patterns at all!
Almost.
The stereotypical classification system goes like this: there are two types of nerd. Type 1 nerds have an amazing ability to focus on their work at the expense of pretty-much everything else in their life: family, loved ones, eating, etc. They will occasionally surface after 36 hours of continuous work to upload some code somewhere. They tend to hold rather strange ideas about all sorts of things.
Type 2 nerds are less focused and more dabbley. They may actually talk to you even if you don't appear to be a source of information for their current project. They are capable of managing people. They are more moderate in their outlook.
There's an interesting side-category: nerds who are intensely social to the point of creepiness, who approach relating to other humans with the same intensity as they would approach, say, writing a device driver. These are type 1s disguised as type 2s.
I don't really categorise people like this, but there is obviously some sort of continuum happening. It's interesting for me to note that at least amongst the people I know, serious type 1s are very rare. I suspect that they always were. It's simply difficult to be that single-minded about anything.