[BobbyH]

You can see why this would work by imagining that you are a Google search engineer that's trying to lower the rank of spammy sites so that quality-ranked content appears higher.

* Spammers tend to have tons of crap sites, so they have less money to spend on registering all of their URLs for a long time.

* "Good site owners" tend to have few high quality sites, so they can afford to spend more on registering their domains for longer.

Thus, you would probably want to use the time-until-URL-expiration as a "ranking factor" while sorting results on search pages.