How you take notes, whether you do so by hand or on a computer, and in what form, is a matter of personal preference and individual learning style, and may significantly vary with the subject matter and style of the course.  Each student must find the method that works for him or her. 

The important thing is that you have a method for retaining the important points covered in class.  Ideally, well-crafted class notes should help students discern the importance of the cases they are reading, the rule(s) that can be derived from a particular case and its material facts, the development of that area of law, relevant policy concerns, and themes which require additional attention and reflection. 

The process of taking notes is part of the learning process for most people -- writing down the material that is discussed in class helps reinforce it in your mind.  However, looking it over later and thinking about it in light of your reading is another way to absorb the material, before it is time to study for a mid-term or final.  Your notes also are the only written document you will often have about the points and developments your professor intends to stress and will most likely expect you to focus on in the exam.

It can be very helpful to read your notes after class, before the next class.  Sometimes reading your notes over just before the next class helps to put what you are learning in perspective.  Coming up with some kind of shorthand for familiar terms used in the class makes it easier to take notes quickly. 

For more information on how to get the most out of your law school classes, see:

Michael Hunter Schwartz, Expert Learning for Law Students (2005)

Ruta K. Stropus and Charlotte D. Taylor, Bridging the Gap Between College & Law School 41-51 (2001)

Dennis J. Tonsing, 1000 Days to the Bar--But the Practice of Law Begins Now (2003)