In my site I haven't used any 301 redirects to solve the www & non-www thing as such my site appears with both urls--- i.e with www as well as without the www. But I set the desired domain with the WWW through webmaster tool. Till now I didn't come across any duplicate content issue with the site. What I wanted to know is --- is this okay or should I've to resort to 301 redirect for my site.
I would suggest to use 301 redirect. I don't think it would hurt... Google webmaster tools allows you to specify the preferred domain name (ex. either www.domain.com or domain.com)