I see the glossary as a powerful tool for enabling student collaboration, peer review, and community building within the course - as well as the traditional sense of defining concepts in a more meaningful way by the instructor. As the glossary can also be exported and imported (reused) over and over, this is a brilliant tool! [as opposed to creating a wiki for the same purpose as the wiki can't be reused over and over w/o restoring entire course w/user data]
Also, with the workshop activity gone from version 1.9 (it was also a little clunky to setup by the instructor!) this still allows for peer collaboration and review instead of just using the discussion forums - and it is indexed!