I have had a policy of not accepting "friend" requests and "Linkedin" connect requests from people I work with for a while.. it is nothing personal.
I use FB to run global projects for volunteers like my Wojtek the Soldier Bear ( www.facebook.com/groups/wojtekthesoldierbear ) project and I always accept requests from people I can see are connected to this world..
It has the bizarre effect of me accepting people as friends I don't know and not accepting/rejecting people I do know and like (if we work together) and people I know see me become "FB friends" and "Linkedin" conntacts with strangers when I am not accepting them.
On top of this, I have mild prosopagnosia which means I often fail to recognise people who I know and completely forget who people are quite often.
Sometimes I make an exception.. if we are working together on a project that uses FB as a tool....or there is some compelling reason to break the rule.
If I don't accept your friend request it doesn't mean I don't like you and if I have accepted a friend request doesn't mean I that I know the person who I am "friends" with at all.