How to Get Dofollow Backlinks from Social Bookmarks?

Dofollow backlinks are very useful when it come to seo,and when you do off-page seo. It is a crucial part of page rank algorithm of google that brings life to your website and make google pay more attention to you. They can guarantee you first page in search results.
Now imagine that you get dofollow backlinks from social bookmarking services spacially when it come to Facebook, Twitter, and Digg...


Today I installed an extension on my Chrome browser that made it easy for me to check if which link is dofollow and which one is nofollow? you can download it here. This extension show nofollow links as red highlights. Now I want to make an experiment and check links from social bookmarking sites.


Facebook
These are my results with facebook, nofollow links every link on facebook is nofollow, however this is what i saw.

links on facebook 

Twitter
and this is what I got on twitter.

links on twitter

Digg
Let's go to digg.

on digg also nofollow links

dofollow links on digg

Yes You'll get a dofollow link for every story you submit to Digg this means you'll get dofollow links for every internal page that you have on your website. As well as targeted traffic that you get from digg.


Bonus
I have found some great dofollow social bookmarking services that can make this post richer.Enjoy
http://www.mister-wong.com (pagerank=8)
http://sphinn.com (pagerank=6)
http://tagza.com (page rank=5)
http://www.plime.com (page rank=5)
http://soforce.com (pagerank=5)
http://buddymarks.com (pagerank=5)
http://www.feedmarker.com (pagerank=4)
http://tamilers.com (pagerank=3)
http://www.ziki.com.au (pagerank=3)

Here I just listed social bookmarking site with high pagerank If you know some dofollow one with good page rank share the love.