It'll hurt when a competitor does a backlink analysis, and ties your website to your DP name. Then go through your itraders and buy all the backlinks that you've bought. Not to mention giving them an insight into all your blackhat methods you've been using/posting about
Guys, DP links are all nofollow. They may not look nofollow on the page, but they are. There is probably an internal robots txt file that disables all links. Otherwise, it is gonna affect Dp worsely. So, I don't believe any link would hold any weight whatever. Also, I didn't see any of these links showing up in my Google link search for my blog. So, no use with it. No issues having thousand links from here.
I think you'' find google will consider your whole link profile instead of just every link individually. If all, or the majority of your links come from topically unrelated websites then you may be penalized, otherwise it should be fine.
dp links aren't nofollow, i don't know where you are getting that info from. i also see them showing in webmaster tools, and yahoo site explorer.
you said it! in fact, I always try to follow my competitors' foot steps online. I personally never use any reference to my best sites on this forum, at least not in a public way.