Men and women do a full body scan of women. It's been studied. Women are actually more critical of other women and compare and objectify their parts more aggressively. Men look not for comparison, we notice women who are attractive or have an attractive body and then look at either what they have on display because they want it looked at (stomach, tits, ass, crotch, legs), or we scan to just generally enjoy the look of her body as it moves. Women are aesthetically pleasing to the eye and being that we are visual creatures... we absorb it as much as we can while we can because once it is gone... we quickly forget about it.
It only takes a second, so yeah. I think for most guys it's face, boobs then finally bum when they have walked past. Personally, I look at all women but am a particular enthusiast for a Beyonce-esque thigh / butt.
Nah. I've done it before, but I don't always do it. Most of the time I won't. Yeah I'd only scan her body if she's attractive, but again I rarely do that. I usually just go part by part at different times.