The Biggest Question causing deep impression on Google Search text box is
"Posting URL in Yahoo help increases Page Rank?"
The Answer will be a NO (I mean a big No).
Posting your blog, website links will not yield you back links. They are categorized under the tag.
"Pages Containing your site link".
This is in no way considered even as a No Follow Link.
This might increase you page traffic and increases number of users who visit your site.
The Still your page rank will not increase.
Page rank will be calculated based on the Number of Back Links that your site gets(except no follow)
Yahoo answers provides no follow backlinks. So how many times you write your blog address in yahoo answers, it just increase direct page traffic.
Yahoo Answers increases traffic but does nothing with page rank.