Forum sigs used to be worth a lot more in terms of weight and PR parsed - nowadays I personally wouldn't give much thought to any benefits to search engines excepting as an afterthought. If you get something from them - great - but I wouldn't put money on any particularly large effects even in the longer term. I've written about this before, but it's worth pointing out the human user advatanges of having a signature that describes your sites, is certainly significant on high traffic forums.
I never vested much into forum sigs.... until i posted a site one time and it was indexed by google a few hours later and out of the sandbox a few days later...
I think it's better to have been there and dropped than to never have been there at all. You seem very smart Shannon. I think I like you. We had a disagreement in an SEO forum but to be honest I agree with lots of what you say. I also use copyscape and it's a great tool. btw here is the BEST advice I have found on how to deal with those that have violated your copyrights. http://www.seologic.com/faq/copyright.php