<p>Does filling out HTML meta description/keyword tags matter for SEO?</p>

Google will use meta tags, but the description, to better summarize your site.  They won't help to increase your page rank.
See:
http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=79812
EDIT
: @Petr, are you sure that meta tags influence page rank?  I am pretty sure that they don't, but if you have some references, I'd love to learn more about this.  I have seen
this
, from the Official Google Webmaster Central Blog, which is what leads me to believe that they don't:
Even though we sometimes use the
  description meta tag for the snippets
  we show, we still don't use the
  description meta tag in our ranking.