Single sign-on / alternative authentication has been a highly desired feature from Ning in the past, and will potentially allow institutions and organizations with existing membership bases to incorporate access to Ning into their existing services. It seems like there will be a couple of other somewhat intriguing options here as well, including logging in using Facebook or Twitter authentication. What's not entirely clear in the material--or, according to John, to Ning yet--is if these features will be included as part of the Pro service or an extra fee.