I honestly wouldn't notice if someone unfriended me, unless it was one of my closest friends. I have about 8 people I interact with on a regular basis. Other than that, I mostly just see people in my news feed. I suppose if I stopped seeing them show up, I might notice, but the news feed travels pretty quickly these days, so I really probably wouldn't.
I don't worry about it if someone does, but my mom has a friend who EVERY DAY goes and looks at her friend count. If it changes, she goes through and searches until she finds out who unfriended her. It's almost obsessive! Lol.
I go through and weed out my friends list about every 3-6 months. I just hope that none of those people are going to get upset now if they see me gone. I tend to keep people who I am close with now, or who I may need to get ahold of for school/family/etc. I delete people who I used to have classes/school with, or who I really don't talk to much anymore.
Who I was when I got my facebook in '06, is NOT who I am now. My connections have changed
