M.D yes i know most of social bookmark use no follow.
But what does no follow means?? No follow means, as you get more voted and came to front page, it is PR7 or PR8, and you wont get passiong PR. thats all
But you will get backlink, and it will help your seo ranking as well traffic.
i think you are new webmaster or have little knowledage about these kinda type.
use my social bookmark service, then after 1 week tell me, if im wrong:)
cheers buddy