hi last couple of months i am analyze google for one of my few websites, google hardly count 30 backlinks from my 500 post reply. so foum posting would be really helpful me in ranking, traffic, backlinks
i think that forum sig links are count in some way when they are dofollow. but there is a lots of links in forum pages with unrelated links and the page content are unrelated to the links. links from forum sig are count, but not as much as you think.
Every 'DoFollow' back-link are considered by Google, unless it's from a banned or blacklisted website
Also try SEO for Firefox extension. It will show them as well. Google is becoming a very picky woman lately.
Forum links are counted but they are devalued and therefore don't carry as much weight as a 'normal' backlink.
There's no 'ideal.' Post as much or as little as you like. Obviously the more you spam out one place the more likely it is the links will simply be discounted (and you get banned from the forum). In any case, look back at the archives of this forum and see what the PR is on any given page of an old thread. It won't be much, if anything at all. What does that tell you? e.g. http://forums.digitalpoint.com/showthread.php?t=10