unavailable titles should have "unavailable" in URL
Pages for unavailable titles should redirect to a URL with "unavailable" (or some other clear indicator of unavailability) in the URL, so that when the title pops up in search results, the user can see that we don't have it before they click through to the store. Clicking through to a search result that turns out to be unavailable is frustrating, and we don't want people to associate the store with the experience of frustration.
Something like http://vbz.net/unavailable/[cat page URI] would work.
This might even be leveraged to reduce CPU, e.g. maybe "unavailable" pages could be static or heavily cached.