Our scout troop uses it for ground clothes, both under and inside the tent. The inside cloth helps protect the tent floor from the Scouts. Wash it in a front loading washer for 10 minutes without soap in your washer to soften it up. Hang outside to dry. This makes it easier to stow. Cut it a little bigger than your footprint as the wrinkles from washing will shrink the dimention. (It doesn't shrink the material, the wringles pull the edges in towards the center a few inches.) I've always put the printed side down as I recall reading somewhere that the exterior side is better at blocking moisture.

ScoutGear sells precut ground cloths (http://www.scoutgear.com/as709997.html)

AntiGravityGear sells it by the foot for ultra-light backpackers. )
http://www.antigravitygear.com/proddetail.php?prod=TYVEK)