Re: probably a REALLY bad question
If it's part of the download service, then I'm in. I want to play 1.07 without the cds, but I suspect that the download is already patched to 1.12.
I'm quite sure that it's only patch 1.12a that doesn't need cds.
As I said, I'm sure it's legal (and honest) to resell cd-keys (so even if blizz didn't like it, there's isn't anything they could do about it), but I suspect that some purveyors are not honest. If I was in the market for some cd-keys and I found an ebayer that was selling only one set (not a batch of 50 or 50 separate auctions or something), then it might look legitimate. But, I wouldn't buy them from a site that does that as a regular thing. I'm not sure why, but it seems more likely that that would include illegitimate cd-keys. I don't think there's anyway to find out without wasting a lot of Lincolns. (I hear it's 5 bucks per cdkey set, and it takes a lot to be statistically significant.)
Edit: I agree that Blizz doesn't care about people reselling cd-keys. That right is expressly given to the licensee in the EULA.