I've no idea if this is the right place for this or not, but Im buggered if I could find anywhere better.
I'd like to suggest a feature to allow you to make private notes on a users profile, visibly only to the person making the note. The circumstance Im thinking of is for when you blacklist someone and want to remember why you did it. Often I find there are people I would play against, but not with and currently its hard to remember the difference with just a simple B.