Same here. One of my websites' index page almost disappeared. After some research, I found out that another website had stolen some of my content copying it so grossly that they even left some links to my site (all my internal links are absolute). The stolen content is not from my index page, but their site comes up first for very specific searches (long phrases copied from my internal pages), whereas mine is in supplemental results. I have reported the matter to Google 4 days ago, and I am still waiting to see any results.