Google's Supplemental Index

Pages in google's supplemental index aren't penalized, but they may as well be. The supplemental index consists of pages that are deemed to be similar enough to other pages, that they don't appear in the SERPS. No penalty, but no traffic to those pages, either. If you find you have a lot of pages in supplemental hell, you know you're losing a ton of potential traffic.

Problem is, you can't do a simple search to find out which of your pages are IN the index from hell. Whereas google used to show you on a simple search of "site:www.mysite.com", it no longer does.

Here's how to find out what pages you have in the supplemental index: A great find! Supplemental Index Ratio Calculator

What this calculator does is find out how many pages your site has indexed in google's database, then Finds the total number of pages in the main index and does the math to find the percentage.