Panda 21.5 sounds good.
Well, I'm making the changes today - I'll write back here in a few months, I too assume nothing much will come of it. This does simply appear to be an algo change that harms the bigger UGC/Forums in general.
My guess: The advice we're getting is meant for 'article' sites / blogs - that's why it's just not 'adding up'.
Please contribute to that thread, it will help get this issue some light. My bet is Google slipped up a little with panda 21.5.