This is a pretty rare coupon as David usually only offers 15% off. So, if you're looking to buy, now's the time. I need to stock up on some new buffing pads!
Edit: Dammit. It looks like they no longer carry the grey block clay. I like that it was a little more abrasive than the green.
One other thing--if you're looking for microfibers, check out www.pakshak.com. Before you order, send an e-mail to Ranney and ask for the Autopia discount. It makes a good deal even better.