Early this year, I bought a wacom bamboo touch and pen tablet at Harvey Norman. I've found it extremely useful for some of my units where it allowed me to jot down handwritten notes, mathematical questions/solutions, formulas, diagrams and do quick annotations on a pdf file without having to print out the lecture notes. It's not hard to write on the wacom; the tablet is sensitive to the tip of the pen so you don't have press down hard on the pen. The tablet is very accurate and smooth, almost like writing with a felt pen on paper. However, when you are handwriting notes, you have to consistently look at your monitor since it's really easy to lose coordination of the pen pointer and as a result, there's a high chance that you will overlap some of the letters or write unaligned. I don't recommend the tablet if you plan to write down large amounts of text in a short amount of time; anything more than three lines (A4 page width) of handwriting will get messy and time consuming. It's designed best for quick annotations or short handwritten notes.
As for the size of the tablet, it's really compact and light - the dimensions (length and width) are no larger than the size of a 12 inch laptop and thinner than a 64 page notebook. I normally leave my tablet inside my 13inch macbook, as in between the keyboard and the monitor when carrying my laptop around. When taking notes, I just leave the tablet on top of my keyboard and trackpad since there's no desk space and since my tablet has touch functionality, I don't have to use my laptop's trackpad to control the mouse - I just use the tablet as the mouse. If you do plan on getting a wacom, I would recommend getting one with touch functionality because it can be handy when you don't have desk space.
If you have any other questions, don't hesitate to ask.