few general formulas

[nix85]

of course there is positive and negative work
positive work being accelerating the object
and negative work delecreating it. neither is
relating to gravitational potential in particular.

work is change in energy, inertial, thermal, gravitational,
mechanical, electrical.. any change in energy of the system
is work.

"If you move the book at constant speed horizontally,you don't do any work on it, despite the fact that you have to exert an upward force to counter-act gravity."

to move the book at constant speed you must first accelerate it
and then work against friction, thus you are doing work,
that you have not lifted or lowered it vertically is irrelevant

[lancaIV]

Yes,You remarked the point : ' ... constant ...' versus Your state ' ... accelerating ( or decelerating) ...'

But between these physical states ' no/work' is the gain potential !
There is also inside the ' phase shift' : how is the Lorentz force,the Coloumb force, orientation/influence  ? (!)

To Your last statement the question : can accelerating not be negative work and decelerating positive work ? ( !)

Thinking from the ZP-Minkowskiraum 

[nix85]

pushing an object is work, on the floor or in space

accelerating negative work? maybe in antimatter universe

[stivep]

If you move the book at constant speed horizontally,you don't do any work on it, despite the fact that you have to exert an upward force to counter-act gravity.

really? ??

to move the book at constant speed you must first accelerate it

pushing force does do work
https://www.khanacademy.org/test-prep/mcat/physical-processes/work-and-energy-mcat/a/work-can-be-negative

Wesley

[nix85]

lanca clearly confused work with gravitational potential