[Brian Turner]

Signature links used to be great for Google until around September 2003, when they were extensively devalued. Now they are weighted very poorly.

I do still use signature links, but namely for human clickthroughs - they aren't a strong way to get traffic, but if you use enough forums you can attract curious people - especially those who have just joined the forum you're posting in, and are happy to join new ones.

2c.