For me it's 99% aesthetics/vanity and I'm willing to admit it. It does however make a difference with road rash as I've had the occasion to find out a few times. I actual like the feel too, call me odd, wouldn't be the first time! As far as aero goes, any advantage would be negligable to nonexistant although the sensation of the wind on fresh shaven leg should be experienced before knocked. In our club about 25-30% of the guys shave, mostly ex racers and the somewhat older crowd.
I shaved for one season many years ago when I was doing a lot of time trials. I do not think it made one bit of difference aero-wise. But it did feel elegant when you slid in between the sheets at night!
Might go do my whole body this minute, come to think of it.
I quit shaving (my face) about a month ago. I said something about it and the wife made me trim it instantly. I asked if I could shave my legs and she said whatever floats my boat. I'm whipped.
Oh now boys...trust me, freshly shaved legs are HOT! Very, very sexy-from a female's point of view. I have also heard that after a long ride, it is much better to get a massage on shaved legs, than on hairy legs. How I see it, men that shave their legs, are seriously into cycling...and are HOT. Did I mention sexy too??