I have been on kariva (generic mircette) for about 4 years. I would say the first 2 years my periods were the same as before i started the pill. (about 1 normal/super tampon every 6 hours for about 4-5 days) The only difference was with the pill they came every 28 days, and before the pill it was every 35 days (kinda sucked at the beginning getting them more often). Then over the course of a year they started getting shorter and lighter. Now I use about 1 light tampon every 6-8 hours for 3 days.

Another difference between a real period and a withdrawal period:

A real period is your body's way to get rid of an unfertilized egg. In a withdrawal period there is no egg (because you don't ovulate on the pill).