I agree that the spammers ruin everything that they touch.. But social bookmarking is just the latest in a long list of things overrun by spammers.. All the way back to paper direct mail, thru usenet, email, etc etc etc.. They are everywhere because it works.. It makes them money..

As for the side effects of the rel-nofollow, I don't expect to see anyone penalized for their links having this on them.. But I do expect that the loss of links that count will hurt their rankings.. It's no really a penalty, just that they no longer count..

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Steve : Animal Charms Animal Jewelry | Fishing Blog
I'm smelling a whole lot of if coming off of this plan.