Some people recommend to avoid "centrino" - Intel's designation for a low-power wireless-enabled notebook, as it costs more than outfitting a better notebook with a removeable PC card with the 802.11 functionality.

Secondly, I have seen that people have been told they cannot use "wireless inside" notebooks on aircraft, which is nonsense when you think that Lufthansa and now United are offering precisely that on their aircraft.

One benefit of adding a card is that if you shop carefully, you can pick up extremely good, long range, excellent signal strength cards for around $35 USD, whereas buying it "built-in" means you take what you can get.