More consumers went to Web sites to make purchases in Q4 2011 than in the fourth quarter of 2010 -- but many could not complete their task. Some 34% claimed they couldn't find the product they were searching for, while 32% said the product wasn't available. Other significant barriers were unclear pricing and comparison and a lack of product information.

Some of the most innovative search engines lately have been developed for mobile devices. Take the iPhone app search engine Summly, for example. The 16-year-old entrepreneur Nick D'Aloisio built the search engine, which last year raised a round of funding from Horizons Ventures, the private Hong Kong investment firm of billionaire Li Ka-shing -- a backer of Facebook, Siri and Spotify.