Back-links 1 vs. 100

Most of my SEO knowledge has come from reading and participating in a few forums. Most posters include a link to their homepage in their signature, but it got me thinking: if they post 1,000's of times, what will Google make of their back-link? What I mean is, if a poster who uses his homepage in his signature makes 1,000 posts on the same site, wouldn't Google see this as spam? (Certainly it would if they were posted all at once, but we're assuming the posts were made over a long period of time). If a back-link is considered a "vote," then how many times can one site vote? And furthermore, if multiple votes are cast, do they count?

If I had to make an educated guess, I would say that the more links that are found on one site, the more they're devalued in the eyes of Google. So if I were to use a link in my signature, I may use it a few times with different anchor text, but then I'd remove it from my signature. Of course, if I wanted to drive traffic from the forum, this would be dumb, but for SEO purposes, I'd assume that 5 links with different anchor text would carry the same weight as 1,000, even if different anchor text is used for all 1,000.

It should be noted that the same theory would apply to a blog. If you have a link on a blog's index page, if the blog is archived frequently, multiple back-links will be created. So if you thought you had a big-time back-link from a blog, it may be devalued by Google with every archive.