I cut my son's hair when he was six months old:-) I really like the trim look on boys. The current hair style that I see many have (70's looking) is one of my least favorite styles. It doesn't mean I think boys have to have buzz cuts, but I definitely like a clean shaven head on a boy.
Recently my son (4 years) had his hair longer on top so he could do a messy look, and it was shorter on the sides - not buzzed, but it was definitely shorter. He likes to wear it all sticking up and messy...a little like Ryan Seacrest maybe, only longer on top?
I haven't felt the same as you about little boys and long hair. It's never been something I have had a desire to do, and honestly, when I see little boys with longer hair, I want to shave it off (hehe...and I don't mean that insultingly to you!). But I do have friends who have done the same as you, and some of them cried when they cut their son's hair. I think it can be a rather emotional thing for some moms!
My hubby had long locks as a little boy. Probably up to age 3-4 or something. It looked too girlie on him. Very pretty hair, but it wasn't a boy hairstyle. He hated it (not then, but looking back on it) and very strongly wanted our boy to have a very definite boy hair style. His mom LOVED his hair like that, though. It sounds much girlier than your son's hair.
I find that I think my son looks cute no matter what his hair looks like. So, while you might feel sad when his hair is gone, I think you'll enjoy (on some level) seeing whatever he ends up looking like with the new hair. But for you it might also mark the passage of his baby years, and that itself can be quite emotional.