Get over it. You're not doing anyone any good, yourself included, by worrying about whether facebook or twitter get some pagerank.
Don't try to outsmart the search engines. It's a silly waste of time, and it's ultimately futile. They've each got a myriad of engineers working on algorithms to sift through and categorize the web in the most meaningful way possible. By deviating from the norm in an effort to outsmart them, you're not only preventing accurate cataloging of your site, but you're throwing off their numbers, putting anomalies in their data, impeding improvements to their algorithms, and ultimately putting your site at risk of being blacklisted.
And if that happens, you will have exactly 0 link juice.
ADDENDUM: It's also notable that these engineers are all smarter than you. If there isn't already a trend in hiding links, there will be. And these engineers will not only notice the trend, but they'll promptly adapt to it -- if they haven't already.