... or vice versa.
First of all, it's good for SEO.
Second of all, I am always logged in to the 'http://www.bcsportbikes.com' version of the site, and when someone (okay, Sky) posts a link to a thread on BCSB without the 'www' (ex. 'http://bcsportbikes.com/forum/showpost.php?p=1096327&postcount=72') that page does not have me logged in (cookie domains issue), and attachments do not show up.
It's a simple 2-second solution by updating the .htaccess rewrite rules: http://www.trevorfitzgerald.com/2007...-301-redirect/
No excuses not to do it!