Painting is one of the quickest and least expensive ways to improve the looks and value of your home. Plan on spending at least as much time Prepairing as you do Painting. Painting alone will not cover a multitude of sins. If you paint over bumps, dents, nicks, cracks, or other imperfections that are part of the surface the imperfections are still there.
Make sure if you are hiring a contractor, that they are going to do the prep work you are expecting. Not all contractors are the same and the prep work is the most important part of the job.