brenno, everybody knows that you are forbidden from selling miles from your account. I think that these mileage certs are a different animal. They technically are not "miles" until they are credited to a SkyMiles account. I don't see how DL is harmed by the sale of these certs - - DL has already been paid for the cert by the merchant or vendor that issued the cert.
nostresshere, I think that you vastly underestimate the number of infrequent flyers/"coupon clippers" who collect FF miles. To those folks, every mile counts. Although $20 for 1,000 miles may not ba a bargain, if you have no other way to get the last 1,000 miles for a free coach ticket for your a vacation that you would not otherwise be able to afford, then it's a steal.
tummyg, yes, that is obviously how RPU got my address. I wonder, though, if contacting a prospective purchaser is not in and of itself a violation of eBay's rules.