It looks like there’s an application (actually a library, I guess) that’s using cairomm already. According to its website:
Papyrus is a 2d C++ scenegraph library that utilizes the cairo library to perform drawing operations. In this respect, it is similar to the Gnome::Canvas library.
It’s good to see people start using cairomm. Hopefully we’ll get some good real-world feedback once more people start trying it out.