Google has long fielded complaints of sign-in requirements associated with Google Play Games. The Google+ requirement and multiple sign-ins required for multiple games has been a hotbed of frustration. Google announced the end of both requirements as part of a Google Play Games API model change.
The Facebook API saw huge changes in 2010 that moved the service away from being a closed network and towards being a more open community. The leading social network site must be doing something right on that front. Facebook was the third most popular service for use in new mashups last year, nearly doubling its total number in our directory.