Hi, check out this blog post by Fredrik Haglund: http://blog.fredrikhaglund.se/blog/2009/02/15/episerver-seo-reduce-duplicate-content/
I had this exact same situation. Blogged it here.
I'm implementing both to make sure it is all covered.
Currently I am developing a multi-language site that defaults to English language so it allows the request of http://www.xxx.com/ and also http://www.xxx.com/en/ .
It does its job, but the site has had a bug registered by an SEO expert saying that we now have page duplication because of this.
Is there a way to enforce the addition of the /en/ to the url?
Do you have any way around this?
Thanks in advance.