In the past I have advised (for good reason!) not to use sleep and hibernate modes on machines used for retouching.
However, considering the price of electricity these days together with the fact that LCD screens reach a stable state much faster I think there is some room to use these power saving states.
Use with care, if your going to lunch then hibernating the machine is fine, if you know that you will be doing some critical colour work on images in a short while then dont sleep the machine.
Clients who run large batch processes overnight are advised not to use power saving as this will compromise the process.