While i totally agree social bookmarking website is a good and fastest way to get your site index quickly but i do not that we could also get high PR for site too although i tried to do this before but i only get only pr 2.
Social bookmarking is most demanded and hot feature and that is most used in the internet marketing. It's also a good way to make your site index fast in the search engines and as you are asking to get the page rank form the social bookmarking, it's true also. If you bookmark your site on various do-follow social bookmarking site, then surely it would be counted by the Google and your page rank would be increased.
It all depends on whether people actually follow your account and how many people are friends with you. It's a bit like Page Rank in websites affecting the quality of the SEO juice passed on by links. Google recognizes whose accounts are more valuable than others. Just remember that you can't do anchor text there. Should be part of your marketing mix.