Is un-friending cool now or something

Is it just me, or is "un-friending" on facebook some kind of new trend?
I keep saying Statuses like "I'm having a friends cull tonight, bye losers" and so on. Why do we feel the need to "tidy up" and delete old friends?

Obviously, I've just noticed I've been deleted by an old friend... I bet they thought I wouldn't notice, but I did.

Anyone else noticed missing friends?