FlickrNet is a .NET library for implementing all of the Flickr API's methods. It is designed to reduce the complexity of calling the API, especially with regards to authentication. This library can be accessed from a variety of frameworks and is written entirely in C#.
The most significant recent development for Flickr has been the introduction of video into what used to be a photo-only service. The API has been updated with new features that should appeal to developers.
Flickr has added more real-time goodness to their photo API. Using a publish / subscribe (PubSub) system, developers can now receive real-time updates across millions of photos across Flickr friends, Flickr Commons, and by tags and geo-location using the Flickr Real-Time API.
If you're looking to run a successful developer program, you should probably pay attention to Mathys van Abbe. He's the founder of Mobypicture (our Mobypicture API profile), which has just celebrated its 500th developer.