Note taking is a bit of a religious dogma for me.
As a chemistry major,I was trained by Dr.Robert Engel something I've found to be very true as a student and has been confirmed by educational psychologists: "There's a connection between your hand and your brain." i.e. writing something out in detail forces your brain to process it.If the notes are good and informative,I find this is very true. Indeed,a good measure of how instructive lecture notes on a subject are is how well you learned from them by taking them down in detail!
That's why to be honest,I'm a little shocked by the responses here to the effect that note taking distracts them from a lecture. How can you be distracted from what the speaker in a graduate level mathematics colloquia is saying if you're forcing yourself to take notes on it?!? Yes,speakers in real time go quickly and of course,we're usually not completely alert and awake-but doesn't that force the mind to pay attention more?
I take very detailed notes along with my commentary. And later-I dissect the notes exhaustively. Or to use Paul Halmos' words;"Don't just read it,FIGHT IT!" And I do. Fiercely. I can think of no better advice to give your students.
There's also a more personal reason for taking notes in a detailed way:Each set of notes is a living record of an experience in your life. It's also a documentation of a personal style of a lecturer-each set of notes is like a personal fingerprint of the author. That relic will remain with the note taker long after the lecture ends.Your memories of the experience will be forever intertwined with those notes.
Now a lot of people here-such as Anton and Theo-are making the case for detailed TeX-ing of notes.Looking at their creations at thier websites as well as the notes made up by my other fellow graduate students,I have to admit-they're making a very compelling case for it. I just wonder about whether or not that personalized element so conducive to learning and nostalgia will be lost once everyone does this.
But once again-the results are VERY impressive. So it's certainly worth a good hard thought.
Those are my 2 cents on the issue.