I've heard the same from Googlers but it does seem that all forums seem to have been penalized by Panda for some other reason. They have not been forthcoming to provide an explanation, only saying that it's not because of duplicated content within the same domain. Since they're not offering any helpful advice I'm leaning toward it being an intentional penalization against forums themselves. Perhaps it's simply a case where forums were given too much preference before Panda. I don't know. Only thing I'm sure about is how much it negatively impacted my earnings.