make sure you spread your links on different forum. i had 300 links in a niche forum and one day it was closed and all my 300 links were lost..... so dont put all your eggs in one little basket !
A backlink anywhere can help, google indexes dp, if DP hits high on the search rankings for a particular keyword then a lot or even most of your traffic could in fact come from DP. It all depends on your backlinks ranking in the search engines.