QUOTE(Kieth.DTM @ Aug 17 2010, 02:56 AM)

I see this question being asked quite a bit by link builders who are in pursuit of backlinks for their sites or blogs. Since its not possible to answer to this question with a simple “Yes” or “no,” I will go over few details below.
Forum link building and forum backlinks can be totally 2 different concepts.
Forum link building would be utilizing forums to build backlinks for a site. In other words, link building using forums with a sole intention of getting the link juice transferred from forum signature links.
Forum backlinks on the other hand can be the produce of forum link building but can be done with only marketing or promotion in mind. For example, you have a site that you want to promote and find some resourceful, high traffic, high PR forums where you post using your signature links so that forum members that are within your same niche can find your signature links and hopefully visit your site. If you post on a related forum using your signature link, then there is a good chance that some forum members reading that specific thread might find your signature link appealing meaning traffic for your site. How much traffic you will get form such promotional activity will depend on how much time you devote in your forum posting, either posting new threads or comment on existing threads. If you are a new member and reply to an existing thread saying “yes, I agree” or “thank you,” then you will be pushing your luck getting someone interested in your post and pay a visit to your site. If you however manage to build a reputation on the forum, make a few friends within the community, and keep posting useful posts, then people will find your posts credible and will eventually visit your site today or tomorrow. As you can see, promoting a site this way requires quite a bit of work but if done successfully, benefits can be outstanding so we can say that forum backlinks “work.”
Link building using forum signatures doesn’t work however. This might come as a shock to some as there is a whole separate industry of forum link builders out there these days. Lots of businesses online that are offering forum link building services only showing the prospective clients how many backlinks they can get form such service.
While getting the backlinks using such technique is not hard at all, how much value such backlinks have in terms of passing link juice is the question. Lets go over some facts which will help us understand the situation a little better.
Forums that allow you to post your signature links usually allow you to post 4 signature links on average with some forums restricting the members by allowing only two signature links where some forums not restricting the members at all meaning you can have all the links you want on your signature. Some are actually taking advantage of such forums by using as many as 6 – 8 links on their signatures.
Now if we look at how many comments one single tread has and how many signature links each individual forum thread has, we see that a sing thread having 20 comments per page with each member having 4 links on the signature, there are 80 external links on each page. Not to mention all the Adsense and other external links the forum owners add in an attempt to monetize their forums. It is therefore not unusual for a single page to have somewhere between 100 to 140+ external links on a single page and that a LOT of external links.
Since the value of the link juice is weighted based on the number of external links are found on that page with more value per link from a page with least amount of external links, you hardly get any value for your links form such page.
Another important fact that needs to be considered here which is that a new thread usually only stays on the category front page for couple of hours on a busy forum after when it moved to the inner pages allowing Googlebot only a 2 hour window to find that thread, index it, and crawl each and every links found on that page which is something that doesn’t happen all the time. Since a new thread page will not have any PR of its own, will not have much authority individually, and will not stay on the forum front page for long, having a backlink form such page will hardly pass any link juice if any at all.
Not trying to burst the bubbles for people that are interested in forum link building here. Just pointing out some facts to consider so that all your hard work doesn’t go in vein. Besides, there are plenty of one way link building methods out there for which you don’t even have to consider such method that is hardly useful.
Thank you for putting a lot of time into answering this question which I am sure many members here have wondered about in the past.