I simply cloned the included 1gb micro sd to a 4gb class 6 micro sd. The inluded 1gb seemed to have very slow read speeds which could have been hindering system performance. Maybe its just the placebo effect but it sure seems that my pdn runs a little snappier with the class 6 micro sd card. Has anyone else who upgraded to better internal memory noticed a difference? What exactly gets stored on the micro sd card? apps? system files?