At the moment I can't succeed in making drag and drop work in trunk.
During debugging I filed: https://bugzilla.gnome.org/show_bug.cgi?id=680638
I don't see there cc to add you.
I'll continue looking at this a bit more. I try to drop from a listview on the clipboard. There is never a drag-received signal issued. My guess is targetentries are not understood correctly, but don't succeed in querying those due to above bug.
The gi API is also annoying in some parts expecting lists instead of TargetEntry (on TreeViews) while on widgets you must pass TargetEntry.