I didn't think much about Santa until buying gifts this year, and after talking it over with my husband, we decided we'd go ahead and tell him that Santa is real.
Why? Because we both had wonderful memories of the Santa magic. We used to leave carrots for the reindeer and cookies for Santa--and my parents always made sure that they made hoofprints and partially ate the offerings. A few years, my dad even made "sleigh tracks" on the roof next to the chimney. When I found out about Santa, I helped out my parents a little by playing Santa, myself--I got to be the one who brought down the gifts and put them out by the tree.
There was even something magical about that--there I was, helping carry along a tradition that was pure delight to my younger sisters.
I know there's a problem with commericalism, but I think it's also a time to teach moderation--you can use it as a learning experience and have fun at the same time.