Google is doing some major ungrades, mainly with their Data Centers. Do not get too worried Elgoog I am confident this is only temporary. Some of my pages de-indexed only to pop right back up. Some days I have a PR assigned to every page, today my PR is only assigned to my index page. For me this has been going on for at least 4 months and is getting a little annoying.
Another thing Google is mopping up spam sites. Implementing many new algo’s, filters etc… One very prominent web-site who is a CAP member I noted has been thrashed by Google. Once a PR6 site degraded to a PR2. Probably because of the sites he was cross linking with vanished. I am not a PR fan but serps do matter and having pages removed from google gives less weight to your site, therefore a drop in serps would follow.
Bare in mind this is only speculation I and admitt my expertise in this area is limited. But if you are following the Google’s Guide for webmasters I am confident you will be okay.
hang in there brother!
greek39