Yes, I was wondering about that (whether people and on-line acquaintances in particular could take up different size slots).

I think the "Monkeysphere" article oversimplifies--the conclusions from the original are much less certain. I think there's honestly probably a continuum of caring.

As for how we'd know--from this line of research, you would look at what parts of the brain lit up when you thought about different types of acquaintances. Eventually, if your research got really cutting-edge, you'd check to see if there was any correlation between brain activity and behavior towards these people. :)