You could be penalized technically, though I have not seen this as an issue worth struggling with as far as the home page goes. That is more of a problem with internal pages with variables which cause identical content on pages with different URLS. This more prominent problem at the root level is the issue of your links being counted toward the wrong page. You want all of your incoming link power to be directed at a single page with one set of content. If you do not address the canonical issues you could split your link power amongst the non-www and the www version of your website.
Originally Posted by eddie21leeds