It would be nice to have a way to keep notes about your Friends and "Enemies".
A text field, in the user's profile page , visible only to you, that you can fill in about someone you have played a match against.
So you could add notes like "Hyper aggressive early game", "Always allies with X", "Truce breaker" that sort of thing.
I have been keeping these notes myself in blood, and I'm not sure how much longer I can go on.