I think math is only important up to a point of calculating pot odds
and card odds. In online poker, those things are going to give you the most edge because players move around so much and because you can never really get to know a person or their facial expressions. Even in tournaments, you can get moved around from table to table without enough time to really get a grasp on how an opponent plays.
That said, math will only get you so far, especially in a live game. Even in online poker, where tells
are going to be especially difficult, sometimes (especially if it's a free roll in my case) I just have to go with a feeling as to how I think an opponent will react if I make a certain move, generally a bluff. Knowing whether to play tight or loose, knowing when to and when not to bluff, and even when you can pressure an opponent out of a pot is a result of a lot more than just calculating odds. You can calculate odds all day long, but its when you develop a feeling about how the others will react to certain decisions you make that I think you can really expand your game - but that's hard to do when you're playing against a constantly changing group of players. Then again, the whole reason you make a decision in poker from a tell is based upon the probability that their reaction will be as you assumed.