I have the Ambicom 802.11b card. And yes it eats battery for breakfast, and is HUGE (I don't think the sell my modell anymore, but a smaller one).
But the coverage is awesome. Haven't tested any other cards with so good coverage, I can sit outside and still have good signals...
I have a picture of it next to my Audiovox GPRS CF-card here:
http://www.topdogs.no/dippedutter/im...ox_AmbiCom.jpg