So what exactly does creatine do — should I start taking it?

http://www.naturalphysiques.com/cms/index.php?itemid=153

Creatine will increase your capacity to do work. If you are someone who trains short of your potential, i.e. if the set starts to hurt, you stop, creatine probably won't provide much benefit. If you push to the absolute last rep, then creatine increases that capacity to potentially perform more reps. Provided you push through to perform that additional work, and provide adequate rest and recovery, the result may be added mass.

Creatine will temporarily increase your lean mass and provide volume through "pump" because creatine pulls water into the muscle cells. This is temporary, however, and goes away when you cycle off of creatine, so it is the quality of the training and recovery you have during your creatine cycle that lead to results.

Think of your muscle cells as gas tanks and a workout as going for a drive. In normal circumstances, you never fill the tank all of the way so if you drive until you are out of gas, you only go so far. Creatine essentially fills the tank so you can go farther. 9 out of 10 people I work with don't drive until the tank is empty - in other words, they don't push hard enough to really reach their limits - so creatine for them is a waste of money in my humble opinion.