Data Content Types - Search needs to support the ability to search a wide range of content types include: Text - documents, spreadsheets, etc
This is “focalized” search. However, if one does not know exactly what words to use in the search, then traditional search tools will not help. For those instances, one requires “exploratory” search. See this entry for more information on the exact differences between focalized and exploratory search: http://zylab.wordpress.com/2010/03/26/understand-the-two-different-faces-of-search-exploratory-search-and-focalized-search/ )
Now I know this is not the most exciting topic, but it is worthwhile because the role of taxonomy is becoming increasingly important to the complete search experience as well as the automatic classification of documents in various applications (see also the footnote)