My site has [6 months of] internal duplicate content penalty since Dec 2009 [5 months already passed :)] and current fluctuation seems normal to me.
However I tried to keep eye on some bigshots' position for site: operator.
I found that site:techcrunch.com is losing approx 10K pages weekly!
Matt told in webmasterhelp video that; if you are really high authority site; then we would crawl all possible url from your sitemaps. now, if Techcrunch is losing pages like us, then what else can we do?