When ranking was introduced by search engines, the first step towards recommendation was taken. Ranking is a recommendation by the search engine only based on the keyword. As search engine technology progressed, more and more ‘recommendation’ was introduced. As is well known, one of the most active area in search is to create user profiles and understand their context to understand their intent and then recommend what they may be looking. Of course this is mostly called ranking based on different pieces of information.
At one time, recommendation engines were lot more focussed at only a few shopping sites. But as advertisement started becoming dominant, search and recommendation also started coming close. But that is only a short term trend. In fact recommendation is central to solving the information overload problem. As we all know, information overload is one the major problems created by advancement in information technology, particularly the Web.
I am sure soon we will see recommendation engines become very active in helping recommend each piece of information for a user and become a strong filter. That will mean having a better information about the user and her context and use that in filtering what information should go to which user. This is definitely an interesting challenge for people working on reducing information overlaod.