The first were "on-the-way" types; they'd get a latte or mocha and a pastry, using their laptops while they did (on battery), then leave. Not really any personal contact, just a matter of business.
The second group would do the same, but would generally be friendly with the staff. They seemed to stay a little longer than the above, but it's possible that I only think that because they were recognizable and friendly.
The third group were what I called "squatters". They'd set up at a table like they owned it, and generally didn't care who they inconvenienced in the process. The squatters tended to stay for hours, and tended to try to stretch their coffee dollar; buying drip and adding a lot of sugar and milk, or doing the same with espresso to make a ghetto latte. More than once I found squatters who unplugged a grinder or a coffee machine to plug in their laptop, and then got ranted at when I informed them that I needed the outlet to provide service to others.
My experiences certainly don't prove anything, of course.
It probably also helps deal with some of the more disruptive elements of running a coffee shop with wi-fi, like squatters, torrenters, etc. From my time working at one, I recall that the most frequent laptop users could be pretty disruptive, and didn't spend much more than a typical customer.