This bookmarklet allows you to search Google for supplemental results for the site you are currently browsing (see the Supplemental Results definition in the SEO glossary).

Drag the following link to your toolbar (Firefox) or right click and add to your bookmarks or favourites: Google Supp Pages

This number compared to the total number of pages cached by Google (using the advanced search query site:www.somedomain.com - see this bookmarklet) gives an indication of the overall quality of the site. Check out this post on Aaron Wall’s SEOBook.com.

Supplemental results are a complex issue, but basically pages should be in Google’s main index if you are going to get any search traffic from them.