I'm afraid the DOI system doesn't actually bypass any paywalls. I was simply noting that this particular article was publicly available (most Nature articles are not). A DOI is just a persistent, unique "digital object identifier". It is now extremely common for academic journal articles to have a DOI assigned to them. The DOI for an article remains constant, and resolution from the DOI to the current URL at which the article can be found is handled by the DOI resolution system. The DOI for this article is 10.1038/487407a, and one way to resolve it is to prefix it with 'http://dx.doi.org/'. If you want to read more about DOIs, there is plenty of information at http://www.doi.org./

Link to Nature article http://dx.doi.org/10.1038/487407a (no paywall).

Actually, all +1 votes, whether or not made by your friends (and regardless of their +1 sharing preferences) may contribute to the total +1 count for a particular piece of content.

From google: "Regardless of whether you chose to publicly share your +1’s tab, your +1’s will still be visible to others viewing the content you +1’d. For instance, your +1 could appear as part of an anonymous aggregated count of the people who have also +1’d the same thing"