According to the GoogleGuy, supplemental results in Google SERPs will get a new lease of life. The pages in the supplemental results rank badly and are relatively invisible as compared to the normal documents in the main Google index. However, with the new updation, Supplemental Results in Google will get a fresh look.
 
GoogleGuy has said at the Webmasterforum that,
"Okay, I believe most/all U.S. users should see radically fresher supplemental results now. The earliest page I saw was from Feb 2006, and most of the ones that I looked at averaged in the ~2 month old range. As data gets copied to more places, the fresher supplemental results should eventually be visible everywhere, not just the U.S."