This addon is really great, about the one I use most, right after Firebug.
It's a must have for everyone working with websites and SEO!
There is just one bug, that I really would love fixed. It is, that if "description" in the meta-tag is written with a capital "D", the SiteMetrics don't recognize it, so you need to look up the source.
If you get that bug fixed, it's for sure a 5 star addon!