I think that forum link building would help achieve SERP well: As you can find high PR forums, relevant forums as well. In every niche, forums are available so it would give you relevant links. Most importantly, most of the forums are dofollow. If you regularly participate in forums then it would give you targeted traffic to your websites. These traffics are very targeted any may buy your products and services as they already have known about your quality hence they believe you. Most importantly, forums contents is indexed very fast, even a minute as well. What do you think?
you cant use forums purely for SEO reasons getting backlinks from a forum is a bi-product of using it properly. also, the SEO value of forum links is actually quite low. So if you can put a signature link in there, do it, but don't expect it to work wonders.
Yes i think forum link building is one of the effective part of the link building and it will help you to get the maximum.