I spend about an hour a week driving to a place where I can get free used boxes~ they are okay, but it is, obviously, a hassle. I just saw that starting in February eBay.com U.S.-based sellers get free boxes (!) Lucky ducks:
http://ebaysupplies.usps.com/
As an aside, if anyone wants a free gmail invite, email me and I will send you one, as long as my supply last (I have 30). I have been using gmail for a couple of weeks, and really like it. Tim