The bottom line is that drumming up interest in your website(s) using Twitter and Facebook isn’t going to hurt your PageRank, but it’s probably not going to help it that much either. That said, showcasing your site on your Facebook page, plus having several of those little social bookmarking buttons (Digg This! etc.) on your pages can certainly help build up back links, particularly if you enlist in friends to social bookmark a page in hopes of getting it on the front page of the particular site.

In other words, PageRank “juice” doesn’t flow directly from Facebook or Twitter, but it can cause users of those sites to do some squeezing of juice in your direction if they’re so moved.

Whether this will change with the complete roll-out of real time search with Google Caffeine is debatable. But if you regularly use Twitter, it looks like it can be a good way of hedging your bets, particularly when you’re trying to build up a good stable of back links.