I have noticed that some bookmarking sites have a URL like: http://www.socialsite.com/out.php?url=http://mysite.com The link is the only do follow link and clicking on that link takes you to mysite. My question is: Will link juice flow this just as if its a normal link or not?
It's up to them, actually. If they stop the user at a page that uses javascript or a meta-redirect than it will stop the "link juice". If they use a language like PHP to capture the request, log their stats, and return a proper redirection header then most 'bots and search engines will just see it as a lilnk to your site. So the site has the choice, just like choosing follow or no follow.
Most of the time when sites send the user to a local "redirector" page like the one you described above that logs click-thrus and forwards them to the target URL, the redirector page or the directory where it lives is disallowed via a robots.txt entry in which case it will NOT pass link juice.