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interlinking different domains targeting the same keyword universe can get you penalized, so if you're going to play the "more than one horse in the race" game keep them as independent as possible and know what you're doing and understand the risks.

Hi Ross, Google is pretty good today at figuring out that your site is both "www" and non-www, and they typically do a decent job of giving you credit for both versions. In the old days (pre-2010) this wasn't always the case, and domain authority from one subdomain didn't always transfer well between the two versions, and this also caused a ton of duplicate content issues. That said, it's still best practice to redirect your visitors (using 301 redirects) to one version or the other. (My first ever Whiteboard Friday touched on this issue By doing so, you ensure that link equity is preserved throughout your site and you eliminate the duplicate content issues that result when two subdomain both resolve. Usually, a simple .htaccess file like the one listed above will do the trick.