[Zeke]

I never paint anything but the face of the drawer and I wrap the paint around to the drawer box. If the drawer fronts detach, it's a no brainer. On the cabinet doors, I paint the backside and I wrap the paint around the edge of the opening. No paint on shelves, but I do use a clear sealer on all the remaining wood that is not painted.

This is pretty much the accepted way on all cabinets with the exception of ones with glass panels in the doors. In that case the cabinet box is viewable from the outside. A nice touch is to paint the interiors of such cabinets a different shade.

Your exposed shelving can be treated the same way. Any paint on a shelf should be left to cure for a month before placing books or other similar objects on them. But, after a week or so you can lay down some waxed paper before loading the cabinet. Otherwise you may experience sticking and dents where the edge of the book's cover bore weight on the surface.