Based on 2 years of experience surrounded by fellow compsci undergrads: very few people keep ringbinders or folders of stuff. In fact, most people don't even take notes after the first term.
I can't speak for all unis, but where I study the online lecture notes are of a high quality. Comp Sci lecturers at my uni usually make incredibly good notes - unless they're one of the few who make awful online notes out of laziness or some 1980s theory about correct way to present information. In my case only 2 out of the many many lecturers I've had have been like this. In there cases its probably worth keeping detailed notes for you to read back yourself.
But personally I take a laptop to every lecture, keep the slides open on my computer but have pen and paper in front of me. If the lecturer says something NOT on the slides, I write it down. I also write down stuff on the slides that I find surprising or interesting. This usually helps to reinforce it in my mind. However, I never ever read through these notes. Its just to help me remember it and pay attention for the whole lecture. Also, if the lecturer says something you disagree with, you can google it (although don't be the **** that puts up a hand to tell them you disagree about things all the time)
How you do it is of course up to you. Where are you studying, out of curiosity?
Edit: Also, I noticed that as time goes on people switch between taking notes on a laptop to taking notes on paper. Make of that what you will. I've been given notes that were typed as a lecture went on before, and found them somewhat lacking.