Yes, what TA-t3 said. This is a regulatory setting only!

Setting you WiFi to 10mW will not measurably improve your battery life!

In certain situations it may actually reduce it.

Thats weird, first day i got it, i managed to go from full battery to half in like 1-2 hours. Now since i switched to 10mW.. i hardly notice any battery drain at all...

Okay, so some people are saying it shouldn't matter, some people say it does.
a) Whom do I trust?
b) Would the people who say it shouldn't matter explain why it does seem to matter substantially for some people?

Try it for yourself? The power saving might also be affected by the wlan acces point people are using and it's settings. So different effects to different people.

what does 10mw-wifi means in real life? how far is "too far" on this setting?

for example, when i'm in my room, the router is around 10-12 meters away from me, in the next room.
will it still connect?

The N900, like the N810 before it, has a great WiFi radio and seems to connect at greater distances than my other WiFi devices. But just try it and see if it works for you.

Regarding the power setting, I seem to get my best battery life on 10mW with the intermediate power saving setting. If I use 10mW and maximum power saving, it discharges the battery quickly (oddly enough).

But WiFi depends on your device AND your WiFi router, so each person's optimum solution may be different.

Regards,
Roger

Yes, but you must not forget to take into account the problem user Phantasm reported: It looks like the wi-fi chip may be left in a weird mode after you disconnect. There may be other problems too for all we know. All this could make the 10mW/100mW setting affect the battery drain. But with a proper functioning wi-fi chip it shouldn't. So, all we have to do is wait for a firmware fix for this, and then we can go back to proper 100mW (except in countries which must use 10mW).

It depends what your walls are made of and how much loss there is in them. However, on the basis that the construction of your wall isn't changing, its down to the link budget. 10mW is 10dB less than 100mW. 6dB less signal will halve your range. With 12dB less, the range will be 1/4 of the original range.

So my guess is that with all else being equal, the maximum range with 10mW will be a little bit more than one quarter of the range with 100mW.

I would trust the people saying that it's a regulatory issue. Good WiFi hardware will adapted their transmission power as the current situation warrants. The battery life and WIFI problem which plagues somebut not all people seems to be depends on the Access Points that people are using. And also it seems to be a firmware bug which prevents the WIFI in teh N900 from gracefully loosing contect with access points.

At work we use very highend Cisco WIFI access points. I can stay connected with e-mail, SIP and IM connections running all day with very little power drain. At home, I use a lowend Linksys access point. Last night I got bit by WIFI/batter problem. I had an almost fully charged battery. I less the E-mail app running before I went to bed. My battery was drained in only a few hours. My phone powering down woke me out of a sound sleep. (Probalby going to upgrade my Access Point to something decent running a Linux image ).

ok.. so you convinced me i might have been mistaken when i saw wi-fi at 100mW drain my battery.. so i switched back to that... in 40min my battery dropped 30%!!! switched it back to 10mW and it haven't dropped since.. thats 30min. ago now...

theres no doubt that 100mW setting kills my battery.. fast. i have never seen my battery go down so fast in the week i had this phone. and i spent alot of time on wi-fi and on 3G/edge.