I have also seen huge swings in the past week. My max was over 2,800 visitors in one day at the peak of indexed pages, and today if it hits 1, visitors it will be a lot and indexed pages are down to 290! I have vanished for many terms that I have been n the top 10 for for a year now. It just keeps getting worse and worse with Google. Soon you'll have to have a PR 5+ to get any page indexed! What's worse is that it's taking a year to pass PR down to lower level pages. I have PR 4-5 pages and the pages one level down from them have a 0 for over 6 months.