It all depends on what your forum will offer. If it is the same as all the other new advertising forums that start up then no i won't be active and post but if it offers something unique and is different then yeah i would consider it.
I'll post if the forum offers god professional services and has a nice feel to the community, posting will improve the advertising reach of my blog so of course I will if it draws me in 🙂
I can help post, probably, but I won't be able to set one up. I have a real world job, and I'm just thankful to be able to have time for the forums I am at.
Seeing that a lot of promotion sites offer the same things, you would have to make it unique to the best of your ability. Try offering other types of things that other promotion sites don't. That way, people will see that it's different, and will most likely join it.