It depends on the level of subtlety of everything as well as the individual guy. It also depends on what's up in his life or what he's thinking about.
One girl I dated was mad because I didn't realize what was different about her. I begged a friend to give me a hint. "Look at her eyes."
She had lost a contact lens, and one eye was her usual brown, and one was a beautiful green. That's when I found out that her eyes were actually green. But I hadn't noticed all evening.
Same girl, I noticed she had changed a skirt, I noticed her hair looked different, a different perfume.
But sometimes, you have to not get angry if it's subtle. If you get a teeth whitening, or you painted your nails a sightly different color, most of us might not notice as quickly as if you got a large tattoo on your forehead. We won't notice a 5-10 pound weight gain or loss, especially if we see you a lot.
For what it's worth, I try to notice certain things, but it can be the "wrong thing" on occasion. I notice shoes you haven't worn before, but you actually are wanting me to notice you got a teeth whitening. I notice your eyes look even more beautiful, and you want me to notice that your hair is a 1/2 inch shorter on the sides.
I can't tell you if all guys do, but I know some guys really do notice when girls they like change their hair style or do something nice with it. I know that I certainly do notice when girls have especially nice hair days and I do comment on it sometimes, but I've never heard any of my guy friends ever say anything about another girl's change of hair, so I don't know how many guys out there actually notice it.
I know this guy... every time I leave my bangs to the side and my hair up in a ponytail, he asks me if I got a haircut and always says it looks nice. I always laugh because I always have to tell him that I didn't get it cut. Guys that are interested in you will notice anything different about you. Whether you comment about it or not depends on the guy.
M0st of the time we just want them too but if you got a trim yea he probably wouldn't notice but if you SUPER cut your hair he will and if it looks bad he wouldn't say anything but if it looks nice he might...
I think sometimes girls are too hard on guys, if it's hard to tell or just a trim, we might not notice it too. But I think the reason why girls notice more than guys is because girls get jealous easily and always look at these things.