You can already search your browsing history. Non-centralized personal search engines have a few challenges to solve before they're feasible. 1) The web cannot

You can already search your browsing history. Non-centralized personal search engines have a few challenges to solve before they're feasible. 1) The web cannot support thousands or even millions of spiders/crawlers. 2) Search indexes are (probably?) too huge to distribute. See the commoncrawl project. It's TB for a few Billion pages. 3) Assuming a single crawler collects the necessary data, indexes can be easily distributed, and the search engine software is simple to set-up, who is going to subsidise this effort?