For me, some people notice; others just don't. My Sweetie and BFF don't tend to notice, cause they see me everyday or almost that much.
On the other hand, I saw a friend this spring I had not seen in a couple of month and the first thing he asked me was "Have you lost weight?"
Of course the same can be said for other things about your physical appearance. I wore first blue contacts, then gray ones to work for a week each, and none of my colleagues noticed. (I normally have brown eyes).
Then I wore the gray ones to a camping trip and one of my friends noticed with in the first five minutes, in the dark.
You just never know who is paying attention.