Search engines lack a number of simple and intuitive tools that could significantly improve a searcher's productivity. Some examples include:
Relatively limited qualifier options for refining queries (and the limited options are usually not in a form most users will utilize, e.g. hidden on an invisible advanced search form or using operators).
Inability to filter out or prioritize certain results for specific queries without knowing in advance what should/should not exist.
Inability to share easily one's own research on a topic with others.
The depths of this problem become more evident whenever someone is performing research or seeking information regarding a topic that is not part of popular culture or some significant niche.