As seen at SEOmoz | Google - Please Bring Back the Supplemental Results Query; It's Incredibly Valuable -

Quote Originally Posted by Matt Cutts
Over time, the supplemental results are less and less supplemental and more and more likely to show up for any given query. As I mentioned at SMX Seattle, my personal preference would be to drop the "Supplemental Result" tag altogether because those results are 1) getting fresher and fresher, and 2) starting to show up more and more often for regular web searches. Especially as the supplemental results get more fresh, I'd like to leave that tag behind because it still has some negative connotations for people who remember the previous implementation of supplemental results (which has now mostly been replaced with a newer/better implementation).
Matt gives two other reasons why he feels it makes sense to change the query in the linked comment. The entire page is quite an interesting read on the benefits and drawbacks of the Supplemental Index.

What are your thoughts?