for AT&T phones, you can get a more accurate numerical indicator of the iPhone’s current signal strength by manually dialing *3001#12345#* followed by a tap of the Call button. This brings up Field Test mode. The signal strength bars in the upper left are replaced by a negative number. The less negative the number, the better your signal strength. For a reasonably reliable signal, the number should be less negative than -100. Ideal strength would be somewhere around -50.

No one was willing to go on record but some OEMs did at least admit to seeing a ~20% difference between battery life in OS X and Vista.

You bet!