I just found out about this today from the Official Google Webmaster Blog :
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.
At first i thought i was having a big success on getting out some of my pages from the Google Supplemental Index, but I guess that’s explain why i didn’t see supplemental results label on when querying this site using Google since a few days ago (or perhaps more thought i can’t remember exactly)
In my opinion, it’d be more useful if Google keep displaying the supplemental results label because it really help the webmaster to improve their site even more, but that’s just my opinion …