I've just checked in a few improvements to the gtkmm code:
* Added support for share/ui to path-prefix.h and removed all hardcoded paths in the gtkmm code. You should now be able to run inkscape --new-gui with inkscape installed in either /usr or /usr/local without issue.
* Integrated the new Transformation dialog. Looks much like the original one, but is implemented in gtkmm instead of gtk. This dialog is intended to serve as a complete working example of a gtkmmified dialog.
* Added a bunch of individual icons to share/icons/. This is a mix of .svg and .xpms. This should probably be redone. We now prefer having all icons as svg, and having all of the icons in 'icons.svg' instead of as individual files. These files were done like this simply because in the separated inkscape_gtkmm codebase we of course did not have access to the inkscape renderer; now that the code is integrated, it would be a good project for someone to replace these temporary implementations with use of the inkscape renderer.
Bryce