Ask HN: Search engine crawled by its users?

I'm hearing a lot about search engines of late. Their increasing lack of quality, the complexity in building one.

I wonder if its not possible to have an extension of some kind, in which the users browsing activity is the mechanism by which sites are crawled.

For instance, I'd love a search engine that is the sum of HN users web activity. Perhaps that's one channel of many.

Is this feasible, and does it offer any benefit over traditional search engines that indiscriminately crawl the web?