Depending on how this thing is used (job threads?), you could also scrape comments off of a thread page that satisfy a certain format.

e.g. someone posts

  #HNdex
  Title: Rails developer
  Location: Montreal
  #End

in a thread, they don't have to mess with their profile and sign up for your site (I wouldn't), and they get visibility in comments to people who don't visit your site without having to post twice in different places. Meanwhile you get free authentication and advertising every time someone does this.