I bought a Wacom[cost 12 quid from the local paper] to do the shading in a logo I was painting on something, it worked pretty well but my lack of artisticness showed. Since I have the tablet I have seen posts about using them for CAD, not that I have tried. I think people use slightly larger and newer ones than mine. Mine just has the two buttons on the pen, but I gather some have a menu area on them. With the Wacom I could draw lines far better than I could with a mouse, and I could vary the line width if I wanted.
I get shapes like manifold flanges into the pc by tracing them on white paper with a fine pen and after scanning them I draw over the TIF in cad. I did try the livetrace option in illustrator, I found it slower.