Niki forums are a good place to find work, no sure about a sound backlink strategy
Of course a few forum posts get indexed by Google however due to the inherent way forums are designed they are considered a poor method of generating backlinks. The amount of signature links on any given page is excessive, this added to sidewide advertisment links, the poor way URL's are generated, the way old pages are pushed back and the unfriendly code all highlights this.
As Mark is aware I run my own forum
SEO Forum, it offers very little in terms of backlinks to anyone, it was set up more as a hobby, I just struggle to find time to post there.
I'm a firm believer in having a varied approach to
SEO, simply because the goalposts change so very often, last year alone Google tweaked their algorithm over 250 times, so if I do a spot of link building via forums its simply dropping off a URL in the CP and making 1 or 2 posts, do that a few thousand times on related forums and there will be some benefit, not to the state of your sanity though.
Forums are better for generating work, improving ones knowledge and having a laugh with other Internet junkies. Find the right one with the right people and they are certainly addictive.