How do you handle database mailings?

Just curious as to how everybody does database mailings. Do you send to your entire active database, or do you only do lazy customers?

For three years now, we’ve mailed to the ENTIRE active (ordered within 6 months) database every single month. I’m starting to wonder if I’m wasting my money on those regulars that would be ordering anyway. Not only is it a lot of mailing costs, but it’s a lot of discounts as well. All of these people are already getting box-topper coupons.

Think I should start doing 30-60-90 day mailings only?