I think aiming it down a bit is important. I've been blinded by an oncoming bike once when I was in my car and I really don't think that's a safe thing to do to drivers.

I commute after dark on the highway three times a week so need to light up the shoulder in front of me far enough to be able to avoid whatever may be blocking my path, so I'm in the process of switching to better lights then my old light is going on my city bike.