Nothing is more grating than when a previously social, comfortable place is turned into a caffeinated study hall by geeks with laptops. Likewise, it's awful when a quiet, subdued place is over-run with noisy group meetings. Usually, the owner of an establishment makes it pretty clear what kind of environment they're trying to achieve with their business, and it's your job (as a guest), to respect the owner's wishes.
Some coffeehouses make an effort to accommodate laptop people; others don't. So if you go somewhere and you find that they don't have enough outlets, or no wireless signal, or whatever other annoyance, just take it as a given that they don't want you working there for very long. Whatever you do, don't try to bring your own outlet strips, chair cushions, ergonomic keyboards/mice/laptop stands, etc. to work around the ergonomics -- don't be that guy. If you can't work at a cafe for very long, just take it as a sign that you weren't meant to spend all day in the same location....