I'm thinking Google's monopoly on search could be ceded if they don't catch up in the war against search spammers (people who contaminate search results). I was reading a book this past weekend about Google, called The Search, and it mentions a story about Bill Gross, of idealab fame (think goto.com (excite), eToys.com, etc.) who has come up with a new level of search. There's also an interesting blog post about it here.
Microsoft's goal, 20 years ago, was to put a Micro$oft product on every personal computer in the world. They have achieved that goal, and are now entering the search market. Microsoft, along with Yahoo and Google, are now going to take search to the next level: they want contextual search to be a reality. What is contextual search? Think the computer interface in Star Trek: The Next Generation, where the computer responded to your mood, not just the syntax of the search command itself. Contextual search theoretically allows answers based on intent, not simply the text of what you enter. Think about it: right now, search is essentially limited to a text prompt entry; searching for musical notes, or using a style of image, etc. is not possible.
We're already seeing trends and uses of contextual search: think ads in Tivo recorded TV shows, esp. when consolidated with clickstreams (what you were watching before the show, and even integrating that with what you were doing on your computer the day you watched the show).
Today's google, for example, asks advertisers to bid to display their ads next to a search result. At first, the highest bidder wins the auction, and her ad gets displayed at the top of the list; the second highest payer second on the list, and so forth. With google adsense, within a few days, the ad that is clicked on the most (gets the most clickthroughs) gets promoted to the top of the list.
The newer, better search engines, according to Gross, will use a similar arbitrage system, but instead makes not only clickthroughs, but actual product purchases the criteria by which an ad gets promoted to the top. This is one step in ultimate search: answering a searchers needs, in context, real time, based on the perceived intent of the searcher.
