In my experience people prefer the "I think" when you are unsure of what you say, and to be clear when you know what you are talking about.

Odds are that a person that never ever say "I think" believes that his opinions are 100% right, witch nobody else will like(Mr Perfect) and a person that always says "I think" is insecure, weak, always depending of what other people think about me mentality.

As the romans said: The true is in the middle.