Depends on where you are at in the SEO timeline. I just started and made one comment on a site and now I get more traffic from that site than several of my paid boards combined. If the comment is on a high traffic board and is very relevant that it could pay big dividends for a new website like mine. On the other hand there may be other great ways to continue developing SEO for the long term. For the short term though..this one comment has been gold for my newbie site.
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