There is quite a bit of discussion going on across the net about this SUPPLEMENTAL INDEXING problem that so many people seem to be having. In this article, HowToSpoter explains what their particular situation is and describes the steps they took to put their supplemental pages back into the original Google index.

What is a Supplemental Result?
Supplemental results are generally pages that Google has determined to be secondary to other, more relevant pages that Google has indexed on your website. In effect, supplementary results are actually a secondary database of results that are only called upon when the most obscure queries force Google to check all its indexed resources.

It’s definitely a good read, especially if your dealing with this problem yourself. I have heard through the grapevine that Google is planning to get rid of their supplemental index, but I have yet to confirm this rumor. At any rate, I tried to find a supplemental result for HowToSpoter.com and apparently, they have fixed their problem as I couldn’t find any.

*TIP* To see if any of your sites pages are listed in the supplemental index, type site:www.mydomain.com *** into Google. Replace MYDOMAIN with your actual domain name. Let us know how many results you find by leaving a comment.