Matt Cutts just posted, what I take to be, a very signifcant clue on what to avoid with Hosted doorway pages.

If someone came to you and said “I want to rent out your mail server. I’d like to send out some emails from your server, and I’ll give you $N to do it,” you’d be suspicious and probably say no–unless you wanted your mail server to end up on email blacklists. In the same way, if someone comes to you and says “I’ll give you $N to rent subdomains, subdirectories, or pages from you. Just link to my doorway pages from your content,” I would recommend to say no as well. It can affect the reputation of your domain if you host doorway pages for someone else and then that other person creates spam on the pages on your domain.

That makes sense to me as it’s "you" hosting the domains - so this spam is on your own domain.  What it also suggests is that Google is looking not only at the domain, but the subdomains, and if one of them is preceived to contain spam, the reputation of the parent domain may be affected.

Some of the comments on the blog posting suggested people had differing opinions regarding if this policy is spam or if it’s just being selectively applied.

"I wanted to get it out there so people would understand if we started to take stronger action on this."

There’s certainly a lot of debate on the issue of Doorway Spam. I’m more interested in making sure whatever Google, or for that matter, MSN and Yahoo, comes up with is UNIVERSALLY APPLIED, not selectively.

Don’t punish small sites that don’t spend tons of money of AdWords yet leave along the bigger sites that support Google Advertising. It’s worse on Yahoo than Google, but I get the impression from both search engines that there are 2 sets of rules, one for the paying customers and another set for the non-paying customers. Lets get to the ONE POLICY that applies equally to everyone.