They do count but I am not sure how much. I have gotten PR1 from just a couple of links on here when I first a started a site. Just do not spam the forum to build back links because you will end up banned.
Yes definitely. Dp has a page rank of 6 (Predicted 7) and Backlinks of 86164. (Source:http://www.iwebtool.com/pagerank_prediction ) Moreover, if u post in DP have a signature link back to ur site, u can track how much traffic ur r gaining from DP.
For a good PR, the backlinks has to be from high PR pages for good serp rankings you need to have large number of backlinks pointing to your site from various domains and not just from DP
They'll count, but the links won't be worth much. (Seriously, think about how many outbound links there are in the typical forum thread.) They are much better for helping drive targeted traffic towards your own site though (or in my case, a pair of valuable threads).
Some of these pages (for example, this one) dont even have a PR, so they're not very useful i guess..
I doubt any PR is passed. They do count as backlinks, but the value is very very very small, close to zero. Instead it is good for sending bots more often to your site.
The links from DP has always been good to me. I am getting at least Good Traffic if not PR. I will say signature links are very valuable in DP forums.
Do backlinks from DP improve a site's PR? Do they count? Yes, they do count. Although only to a certain degree because they're coming from the same website. You need links from various higher rated sites to improve your own site's PR.
They do count. To what degree who knows, but Google regularly dispalys DP Sig Links in it's backlinks.