(Just a quickie post.)
The more I see from the Sitemaps team, the more I like them. Here’s a good post from the Sitemaps blog about viewing stats for both www and non-www versions of a site, including a pointer to this support answer about consolidating such sites together.
The only thing I’d add to that answer is one recommendation: check your internal links and to make sure that they’re consistent (either all to www or all to non-www). That will also help search engines pick the root page that you prefer.