I don't honestly know. I don't have any of those social-bookmark tools installed, don't even really use either of those sites, and I consider myself to be fairly geeky. (I dislike such things on principle, so refuse to install them. You never know who's going to put a rootkit on your machine. [Sony, I'm looking at you.])

You might try dropping by some of the SEO forums and asking this question, just to get additional points of view. I'm a sometime lurker at highrankings.com's forum, and there's lots of interesting information there - not just about SEO, but about issues just like this.