Android - Use an Android tablet as a Wacom drawing tablet for a PC?

The GfxTablet project should allow you to do this. It's network-based rather than USB though.

A touchscreen tablet is not like a Wacom tablet. Drawing tablets use a stylus with one or two pressure-sensitive tips and several buttons. The stylus is also sensitive to the angle you hold it at, and the tablet can detect when the stylus is hovering above the tablet, even with no contact. A drawing tablet has a resolution of a fraction of a millimetre. You can wield the stylus like a calligraphy pen, an airbrush, or anything in between.

A capacitive touchscreen such as you get on a Nexus 7 is designed to detect fat blobs like finger tips. It can't react to you hovering over it, to the natural pressure changes you get over the course of a stroke, or to the angle. Samsung's Note series has a pretty advanced stylus, and it makes a nice drawing tool, but it still lacks the advanced features like angle sensitivity.

Sure, you can use a touchscreen to draw and to create artwork, but asking it to replace a Wacom tablet is like asking finger-painting to replace the whole range of artists' paintbrushes. You'll never be satisfied with the results.

The Virtual Tablet app is free on the Google Play Store. It works with some flaws but overall good. See the developers site for more information