Blender got integrated matchmoving / tracking with the 2.61 release, by way of libmv (which I am the BDFL of). A critical part of many tasks in 3D reconstruction and tracking is a solid, flexible nonlinear minimizer. Since Ceres is so easy to model problems with, is so fast, and is appropriately licensed (unlike some alternatives), it is an enabler for these more sophisticated tracking operations.

Note that Blender's next open movie, http://mango.blender.org, is live-action done with Blender's tracking tools. Ceres is going to be used for that as well.

I guess that one application would be camera tracking to implement automatic compositing of 3d models into videos.