I'm guessing this situation is just fall-out from big daddy but I do want to make sure before I spend a few days rebuilding my site to appease googlebot.
I've managed to stay in the 1st, second or 3rd position for my main search term for nearly 5 years up until feb 2006. Not a popular keyword but very valuable to me anyway.
The site was established in 2001. Well optimized and I haven't made any structural changes in nearly 4 years. Its only about 10 static pages. Last year I added a vbulletin forum and its directory is excluded with robots.txt. There were no ranking changes with the addition nearly 12 months ago.
Originally with the big daddy update I dropped to around page 4. Just dropped to page 6 recently so I figured I better take a look around on my site.
I noticed my index.html page has a pr0...but my domain name is pr4 and all of the sub-pages off my main menu are pr3. Also noticed my sitemap was pr0 which was kind of odd.
So I took down the sitemap recently... not a permanent move but just to see if G really didn't like it for some reason. No change since the site has been recrawled.