DP probably lost PR because it has thousands of nofollow links all over the site (the main forums page has all those nofollows to the profile pages for instance). Google appears to be in a phase of majorly punishing anyone that uses nofollow at the moment.
Well DP has been falling behind lately. DB errors, slow loading pages. It's probably the reason why it fell in PR.
I think the hisghest it went up to PR8 According to a few pr checkers its not official PR4 Result DP1 Result DP2 And I dunno but the result 1 says DP only has a few hundred links?
I guess this is because of same content being generated again and again by member. Why my isn't getting indexed ? how to increase page rank ? my payment was not received i have earned $$$ so and so.......
so, now it looks like that no follow has actually drained dp's authority, it did not gave the value to the outgoing links but it just died. may be then dp should just remove the nofollow tags from the profile pages so that it actually reaches the profile links. better than being wasted...
It is a matter of time before dp will bounce back and regain its lost PR. But who cares about the PR. dp is such a big and favorite forum where the knowledge matters more than the PR
to be fair DP doesn't need the PR, it's popular enought on it's own. It's so big that PR doesn't really make a difference.