tedster - 4:20 pm on Sep 21, 2011 (gmt 0)
I'm sure from all the communication that "shallow" content (note - it's not "thin" content) is being measured quite differently than word count. However, there certainly is a chance that a forum post of few words might be seen as shallow.
For forum posts, I'd say 100 words is too high a threshold - go for a cut off of 40 words and see what that reveals. Also see if there are a lot of "fluff" posts on the forum.