Untested code:
* QuickTime is untested: it may or may not work

Promising extractors that probably deserve to be written:

text:
* dvi (creation date, page count)
* man pages (title, modification date, authors, brief description)
* info pages

office:
[Note that for text-files, the language-specific printable extractor
 (-B en) works quite nicely.]
* rtf 
* Microsoft doc 
* StarOffice sdw
* Microsoft ppt
* Microsoft xls

video:
* mpeg
* avi

code:
* Java (@author, @version, classname, inner classes, brief class description)

packages:
* deb 


