Should I be worried about duplicate content?
JOHN MEULLER (Webmaster Analyst from Google):
In general, you don’t need to worry about duplicate content, because that’s more of a technical issue on our side that we should solve on our side. On the other hand, if you’re seeing these mSite URLs in desktop search especially, then that’s a sign that we’re not picking up that association properly between your desktop pages and your mSite pages. So that’s something where I would really double check the implementation there. Make sure you have the canonical set up properly on your mSite pages. Make sure you have the alternate link set up properly on your desktop pages- that you’re doing conditional redirect if you’re setting that up properly. And really make sure that this connection between the individual mSite pages and the individual desktop pages is actually working as you would want. This is one of those situations where using responsive web design or using a single URL dynamic serving has really strong advantages, because you don’t have to worry about individual URLs showing up in different locations or being indexed in different ways. So that might be something to think about if you’re doing a future redesign. Maybe you can move to something more responsive that uses the same URL for the desktop and the mobile pages. In general, we do support the three variations. But we do recommend responsive web design wherever possible, because you save yourself a lot of these hassles of having to worry about what happens with my different URLs? How do they get indexed? What happens if I have links to those URLs? What happens if I have a completely different site structure on those URLs? All of that falls away.