One of the great features of the Viafo platform is you don't have to change your apps when APIs change or alter, you can either add the new API or we'll upgrade the old one. Tumblr is in the process of a major upgrade to their APIs, moving from basic authentication to a more secure and 'modern' oAuth based authentication.
Because this is a significant change and will require users to authenticate in a different way, we've decided to run both Tumblr APIs in parallel for a few months. So we'd recommend going into your apps and adding the V2 API and then later removing the V1 API - remember that's all you need to do, the UI in your app will handle the changes automatically!
We've also taken the opportunity with the V2 API to enable commenting on Tumblr threads through our REPLY API and added FOLLOW to allow you to follow specific Tumblr accounts, all in the same way you'd do it with Twitter.
Facebook Like: We've just finished implementing the new Facebook Graph LIKE function, to map to our existing FOLLOW API - this doesn't work quite the way that you might expect and we'll be issuing a tutorial for this shortly.
Check-In: We're now supporting Unified Facebook and Foursquare Check-In through the same gateway API and we've provided reference code on Github for how you can make use of this in your applications.