This is pretty related to my site. Since I was hit by Panda mid of June, I immediately removed useless pages with less than 100 words. Also did some adjustment, but 'til now didn't see any recovery.
I also have those pages with a single sentence for a question (a wordpress site turned into Q&A) but with around 500 to 1k accumulated words on comments. All in one page. Does G sees it as thin content? Are comment/replies counted as content?