Over the past month or so, Google has been having some issues with its "Big Daddy" infrastructure. The main issue reported to Google was that there was an overflow of "supplemental results" listed in the index. Matt Cutts said that the issue should now be gone," at least within a week's time. I have been tracking the supplemental index issues from early on, you can find more detail from my entries on 03/06, 03/09, 03/14, and today.
What is important to note is that Matt Cutts kind of gives us more insight into what exactly is this mysterious Supplemental Index. Google has their official help page on it, but it was never clear. Matt explains; if the site is not crawled as much as the main index, in Big Daddy, it may result in showing pages of that site in the supplemental index.
With the supplemental index issues almost resolved, the big daddy index should be live within the next week or two, meaning at all the different Google data centers.