How good are the backlinks in the signature area of this forum? I seen some people with thousands of posts and their websites have one or no PR...
Not sure about this one, generally they don't seem to make much difference. However a strange thing has happened to me one time. I gave a good answer a few months ago, and several people quoted the answer and commented that it was a good answer. Somehow Google seems to know this, as this thread is the only one that Google acknowledges as a back link. So perhaps if you give some really good answers, your link becomes more valuable in the eyes of Google. This is just speculation, but you never know!
I think it depends on the quality of the thread you're posting in, not just your answer. Google will index and rank a thread higher on DP that has 2-3 pages of quality responses than a thread with 4 responses and they all say the same thing.
Sometimes it is pure luck. You cant know what is in those search engine algorithm. In one forum, I saw a useless thread having a PR2. Tried to see its linkbacks, didn't seem to find any important links to it. Most of the post I comment on here at DP appear on my Webmaster tool, but i doubt if they really have any impact on my rankings. One thing we should know is that the search engine spiders are not Humans. They work according to the instructions they were given.
To me the benefit of the signature here on DP is to be able to have your site indexed by google not for the link juice. I change my signature every 4 or 5 days so a different page gets indexed. I really do no think that much link juice comes into play but that is merely speculation.
Its a quick way to get a new site indexed, there's so many outbound links on the site I doubt they carry much weight.
I think the best way to get links, is to trade social bookmarks. Try some forums that encourage trading bookmarks and exchanging reviews. Digg and Stumble and all the social sites love it when you get lots of bookmarks and reviews, that includes facebook and myspace. I think it will deliver many high pr sites to your webpages, it may deliver some low pr as well, but it will definitely increase your traffic, for free.
As a normal forum with high thread traffic, I think sigs will not take effect to PR (if that what is your goal).
It will help your new site get indexed fatser. It will bring you traffics if your site is relevant and you use interesting anchor. It will not give many juices though.