outland88 - 8:54 pm on Sep 5, 2007 (gmt 0)
The sudden drop or vanishing of the index page may signify your trouble is about to begin. May go hand in hand with Universal Search. It seems to me Google has decreased the allowable keyword density on index pages to elevate universal site pages in competitive areas. They may also be discounting links to the index page. Many sites such as in travel or niche areas may go unaffected. From experimenting decreasing the density for the searched term may elevate your own rankings but hurt you on long tail searches.