You may want to check the other active thread on thin content. [webmasterworld.com...] There's new info that suggests a 500-word limit could be valid.
You say it's not about words but I skipped all the Pandas until I stupidly reduced forum posts per thread page from 25 to 10 to see if page speed increased. The unaware side effect was spreading my content 'thinner'. 5 days later after a deep crawl Panda 2.4 released and i got dumped.
For my main site I have too many thin pages (less than 250 words), which I want to merge into pages with at least 500 words. My concern is that since my content was copied by other sites, if I merge pages, Google could compare them to existing content on older pages and conclude the other site(s) created it. Then I get hit with a dupe content/Panda penalty.