I made some good progress on breakable joints this week.
All joints and springs will have a Breakpoint and a JointError (or SpringError) value. The JointError is a measure of how "broken" a joint is. The Breakpoint simply indicates the maximum value the JointError can be before it breaks. When the JointError is greater than the Breakpoint, the joint (or spring) is automatically disposed and removed from the simulation. It's a very simple interface to work with.
As I add the breakpoint functionality, I'm also doing some api/code cleanup on the classes. Here is a list of all the joints/springs in Farseer. The items with the strikethrough have the breakpoint functionality added and are cleaned and ready for the release. (note: any spring or joint with "Fixed" in the name just means it is attached to the world rather than another body)
Finally, here is a video preview of the Farseer Physics Engine samples framework. Enjoy!