I admit it - I struggle to understand patent applications (one of the big reasons that Si is part of our staff). However, Bill Slawski doesn't and it's made our collective lives in the SEO world (and the mozplex) considerably easier. Take, for example, his two incredibly fascinating posts collecting patent applications and speculating on how the engines might re-rank the results:

• 20 Ways Search Engines May Rerank Search Results
• 20 More Ways Search Engines May Rerank Search Results

Bill inspired me tonight to give my own wild and crazy speculation on how search engines might use data of all different kinds to help order the search results. Here's what I came up with:

1. URL / Brand Name Mentions
   As the engines find mentions of URLs and brand names in the content of websites, they might actually use that data almost like hyperlinks - considering it as a reference even when the link isn't there. Since many of the best news sites and virtually all of the research papers in PDF provide no link love, this might be a good signal for the engines to consider.
2. URL / Brand Searches
   If a domain or brand name is receiving some volume of searches, the engines could use both frequency and temporal demand to re-rank results. They might even consider associated terms - like if lots of folks are searching for "Tasered University Student Video," the engines might start to rank that intended result highly even for more general searches like "taser video."
3. Link Traffic
   I see no reason why, with the number of monitoring applications (toolbars, desktop search, analytics, etc.) that engines like Google, Yahoo! and (perhaps especially) Microsoft have available, they couldn't use the number of clicks on a link or the amount of traffic driven to a page from another to help rank the value of links.
4. External Registration Data
   Book publishers officially announce book release dates, movie studios set opening days, sports teams file for trades and games, and businesses file tax returns, outlook prospecti, quarterly earnings reports and more. All of this "registration" or "release" type data is public knowledge (at least, a great deal is) and search engines could conceptually use information like this to help to predict demand and identify the official site/pages associated with the material. It might even be voluntary - if you're a business releasing a product/service/etc, one day you might be able to register with the engines the same way you register a local business with them now.
5. URL Mentions Offline
   I know, this seems like it would be hard to track, but in reality, nearly every major TV program, radio show or broadcast message has a script (some before release, others after) that the engines could conceptually scour for URL mentions. Again, this might help to identify demand before it pops up, and to help serve up the right results, i.e. What domain name did Anthony Bourdain mention on his show for Stockholm travel info?
6. Email Content
   Since all of the major engines now have fairly popular email services, watching for URLs and domains in the body of email copy, and using it either in personalized results or general web search might be beneficial.
7. Social Media Activity
   Services like StumbleUpon, Reddit, Newsvine, Digg, Del.icio.us, Google Share, etc. all let you pass content around or vote on it. One day, search engines might try to interpret all the activity and find the signal buried inside the noise - start thumbing up those pages, people :)
8. Site Owner Credibility
   No good bum? Superstar Philanthropist? Maybe the next time you register a domain, the engines will take notice. This might be a really smart idea for things like new product launches - ID'ing a company like Disney buying a domain and making sure it stays out of the sandbox. Or, conversely, finding a domain registered by Dave and keeping it in :)
9. Link Sting Operations
   If spam ever gets really low, and search quality teams need something to do with their time, they might consider making honeypots of paid link sources to help ID potential link manipulators. Just think, one day you might be trying to close a transaction to help rank your Texas Hold 'em / Lingerie / Printer Cartridge website, the next, all your domains have the "you fell for it" penalty slapped on.

Any nutty ideas you've got for factors that search engines might consider using?