yesterday in #maemo (sameo is the official developer of the WLAN driver module at Nokia):

(21:49:56) bhima: I can do 10mW wifi. Mine's been on with wifi on but not much actual use for ~3 hours and hasn't dropped a bar.
(21:50:29) vidaroni: i just switched to 10mW myself.
(22:06:20) sameo: bhima, vidaroni : 10 or 100 mW won't make a significant difference as far as WLAN power consumption goes
(22:07:05) bhima: sameo: hmm. ok. why not?
(22:08:38) sameo: bhima: because the radio frontend is not the major power sucker in a WLAN chip.
(22:08:59) sameo: bhima: in an integrated one as this chip.

Greets, Jonek.