Just out of curiosity did the panda update effect whether sites were using www. infront of their domain or not. whether or not it is still considered two different websites to google or just one?
I don't think Google Panda focus on that part of site, the once and for all simple solution is do a redirect to URL you prefer, with www or without www.
The www and non www version will be always on major issues in SEO. And it is considered canonical issue. Without fixing this issue one can not get complete benefit of SEO.
I just find it stupid that Google would still rate two different sites for content and pr for the "www" issue..