I'm not quite sure when I stopped believing in Santa. It was probably around 7 or 8, but I can't be certain. I do know that apparently I did believe in him at one point, since my parents told me last year that I stayed awake until 1 Am when I was four waiting for him in the living room.
Then again, my belief in the supernatural never really blossomed. My parents never took me or my siblings to church, so there was no chance I would grow up and go "you lied to me about Santa, so you are lying to me about Jesus!".
Will I tell my kids stories of Santa? Sure. Why the hell not. What is childhood without magic or imagination? Without Santa, Christmas would just be another birthday to a kid, another time of the year where they get free crap, and they would lose all the special meaning behind it. If you take away Christmas altogether, then you miss out on one of the great events in western culture, plus other kids would probably make fun of you.