Prashanth Koppula and Matt Cutts at Google Webmaster Central informs that Supplemental pages have now gone mainstream.
"Since 2006, we've completely overhauled the system that crawls and indexes supplemental results. The current system provides deeper and more continuous indexing. Additionally, we are indexing URLs with more parameters and are continuing to place fewer restrictions on the sites we crawl. As a result, Supplemental Results are fresher and more comprehensive than ever. We're also working towards showing more Supplemental Results by ensuring that every query is able to search the supplemental index, and expect to roll this out over the course of the summer.
The distinction between the main and the supplemental index is therefore continuing to narrow. Given all the progress that we've been able to make so far, and thinking ahead to future improvements, we've decided to stop labeling these URLs as "Supplemental Results." Of course, you will continue to benefit from Google's supplemental index being deeper and fresher."
Anger is the tones in the current Public opinion as one user Ichi writes:
"Either give us back Supplemental or totally remove any difference between the two because the only thing that has changed now is that we are now blind as to what is happening. Why get rid of it at all? It is easily the most informative and reliable tool webmasters have to understand how Google views a given page. As for worrying about things that matter, isn't worrying about why a given page doesn't show up in SERPs where it once did or where one thinks it should something useful to wonder about?
The Main and Supplemental index was the only reliable tool we had from Google to determine the health of a given page or site."
Matt Cutts goes further and explains that:
"So the upshot is that if youÃ¢â‚¬â„¢re one of these people who was paying attention to this issue, I think it has already improved quite a bit, and I would expect to see more pages indexed in the coming week or two. Some sites may see improvements earlier than others because of where a site happens to be in GoogleÃ¢â‚¬â„¢s crawl cycle."