Common word tool?

In Google Sitemap (beta) there is a page analysis section on "how the Googlebot sees your site" including 'Common words'.

I assume this is ranked according to the most common words (in which case the most common word on one of my retail sites is 'VAT'!). If so, how important is this information when google ranks individual pages?

For example, will a page optimised for 'copier paper' be penalised because the most common words (on the whole site) are say 'stationary', 'office', 'supplies' etc and 'copier' and 'paper' are way down the common word list because they're only on a few pages?

Does anyone know of any SEO tool that can search my entire website and give my stats on the most common words? (google site map doesn't give numbers)

http://www.widexl.com/remote/search-engines/metatag-analyzer.html This tool may help you a bit.

ok, that's useful for a page, but I was really looking for something similar that would do the whole site (ie. give me an idea of how the site is viewed as a whole).

I'm assuming that when ranking a particular page the SE also takes into account how relevent the page is to the rest of the site?