I'd be careful of overworking the shoulders, as they are also worked when you work your chest or back. So don't do two specific shoulder workout AND a chest workout AND a back workout (working the shoulders 4 times a week, which can actually be counterproductive to buiding strength and size in them, and can lead to overuse injury in this particularly touchy joint). If you work chest and shoulders one day, and at least two days later back and shoulders, that should be fine.
Also remember that muscle doesn't grow without sufficient recovery. So it's best to work the muscle hard, less often, then recover by getting enough good nutrition, sleep and rest, and days off of working that muscle. I had my best upper body results (including shoulders) doing the P90X rotation, in which shoulders are only worked directly once a week (then once again, either because of the chest/back workout, or because of the back/biceps workout).
Instead of working your shoulders more days than other muscle groups, you could do priority training: work the shoulders FIRST in your routine (after a thorough warm-up including some range of motion flexibility moves and some moves to bring blood and heat to the shoulder area--even doing a warm-up weight set for shoulders with very light weights and NOT going to failure on that set). By working them first, when you have the most energy, you will be able to lift heavier, and thus give your muscles more stimlation "to grow on"!
