I love how everyone here is telling you to just pencil and paper. For the past 7 years (through both college and high school), I have taken all of my math notes in Mathematica. Every symbol, even the most esoteric ones, is at most four or five keystrokes. For example, an integral like integral x=0 to inf (x^2)/xbar is quick to enter:
integral template -- ESC i n t t ESC
bound -- x = 0 TAB ESC inf ESC
value -- x C-6 2 RIGHT C-/ x C-5 UNDERSCORE
it's really quick to type, and you'll quickly learn the keystrokes from the character palette. I haven't taken a single note on paper in any of my math classes since about sophomore year of high school.