Tag descriptions in WordPress 2.8 is a very interesting post on how to improve your post keywords (tag description). A good way to optimize the blurb nested in the <meta name="description" content="Specific description to make GoogleBot smile to your contents">. See also my long boring french (sorry) post titled: Une meilleure indexation avec Not at All in One SEO pour WordPress (A better SEO with Not at All in One SEO for WordPress)!  

What about Basics and Meta tag description for tags?

Basics use the tag description as a description when you display the “Tag” context. I planned to add Not at All in One SEO for WordPress in a near futur.

Stay tuned!