A lot of guys do, at least in there heads. Like you, I'd rate a 10...haha j/k. But yeah, I think its almost automatic and instinctual for men to evaluate women they meet for attractiveness, especially when we are young adults. I don't think I've ever used a numerica or letter scale, whenever I find myself doing it, it's either I think she's attractive enough I'd approach her or she's not. Boring and binary but a lot of the cases attraction is subjective anyway, taking myself as an example some countries the women rate me at -2, others maybe an 8 or 9, so a rating is kinda pointless.
Nope. Either she is noticeable or she's not. My brains going to either go hmm... she's kind of sexy/cute or she's just flat out invisible. If she's noticeable, I'll gauge her interest in me from what I'm picking up from her body language. If there's something there I might talk to her if I feel like it. The only time I really think about numbers connected to a girl, is when I want their phone number. =P
I don't think most guys actually use the numbers to say how attractive they think a girl is, but might just use it as a quick reference if they tell their friends about a date they had recently or something... I don't know of any girls that do that often either. Even just in my head, I'll decide if I think a guy is good-looking or not, but I don't actually rate them.
From what I've noticed, it tends to be more-so a "yes" or "no" thing rather than an actual rating out of 10. Some guys though, usually the younger ones, do give ratings when they're out with their friends, yes.