Hello, I was wondering if it's possible to successfully gain link popularity and rankings by getting links mostly from one domain (ie a forum). Would it help if all (or a lot) of the posts have PR as well? I just want to know if I'm wasting my time posting to the same forum if it's not really helping that much. Thanks!
You will gain link popularity, but you likely won't get any good rankings unless you are targeting uncompetitive keywords. When you get many links from the same domain each additional link counts a little less. It is more beneficial to get links from many different websites. Links from forum signatures are typically quite ineffective. You need lots of them to have any kind of effect. You should look into some other strategies like article submission, press release submission, blog commenting, link baiting, etc.
links from forum will not give you any PR anytime soon as all the new posts where you will be posting on will not have nay PR of its now to begin with. maybe you wil get PR1 a year later if you have thousands of posts. if you want PR and SERP result, then you need a mixed link building campaign