Google +1 constitutes a crucial departure for the kind of data that Google will use in its rankings and that comes with an important challenge. To date (almost) all of the data Google uses is from implicit signals. Someone links to another site and thus bestows some authority on that site. Or someone clicks on a search result and makes that result ever so slightly more important than it was before. Or someone has Google’s search bar installed or uses Chrome and contributes time on site signal (also through Google analytics?) simply by spending time reading something. I am saying almost all because Google has had some data from user’s ability to re-order search results explicitly, though I don’t really know of anyone using that. Adding an explicit signal button with +1 is an admission that the implicit data sources are not enough. Clicking on +1 is saying to Google explicitly: I think this is interesting. Now the real challenge for Google will be making this an actually useful signal. That’s hard because of course spammers can click on this as well and/or pay others to do so. The reason that Facebook’s “Like” button and Twitter’s “Tweet” button work well for signal generation is that the action broadcasts to friends / followers. People generally don’t want to spam their friends / followers and it is relatively easy to tell who is a real person. Now in theory with Google +1 you are also broadcasting, but Google really doesn’t have a social graph (yet) on which this broadcast takes place. In the absence of that it will be a lot harder for Google to get signal. This puts a real premium on Google either building or acquiring such a graph quickly.