I've built a SAAS application and am now working on marketing it. There are a growing number of directory listing sites that claim that that listing on them will boost your "domain ranking" and in turn boost your search result positioning.

Do they work?

They seem a bit like the old webrings, all publishing the same content and referring to each other, with monetization added. I would have thought that the search engines were wise to this, but interested in other people's thoughts?