The same patent notes that legitimate domains "are often paid for several years in advance, while doorway (illegitimate) domains rarely are used for more than a year." Registration length, WHOIS privacy and ownership changes remain unconfirmed. What Google does confirm is the site reputation abuse policy against third-party pages placed on a site "mainly because of that host's already-established ranking signals". Hosting guest content is fine; renting out your domain's standing is not.