From curiosity I also checked the GTK3 port of Libre Office ..and also GTK3 port in Gimp and Firefox.
Libre Office GTK3 Port
Ubuntu Quantal ships a libreoffice-gtk3 package which is supposed to be the GTK3 plugin of LO widgets.
I tried it, but I couldn’t see any GTK3 integration to it. So I asked on LibreOffice-dev IRC channel and guys there told me that GTK3 port isn’t ready yet. I Google it a bit and I found the LO GTK3 Port Git. You can see some top class developers to work on it (around 5-6 people), but this Git isn’t very active. However if you want to be optimistic, yes there is an upcoming GTK3 port for Libre Office.
Gimp GTK3 Port
GTK3 in Gimp will arrive in version 3.0 -which comes after 2.10. Gimp roadmap doesn’t give any dates so I asked Gimp developer Michael Natterer (aka mitch).
Mitch told us: “Next stable release will be 2.10, which will bring the gegl port, and deprecates lots of libgimp API. Then there will be gimp 3.0 which will be GTK3. There is the gtk3-port branch that it kept rebased on top of master and works pretty well. The only date i can give is that 3.0 will come after 2.10, sorry”.
I didn’t try to compile Gimp, but that branch seems super active at the moment.
Firefox GTK3 Port
Bug 627699 - Port GTK2 to GTK3 reported in 2011-01-21 by jhorak:
“Very WIP patch. GTK+ 3.0 and GNOME 3 are approaching and we should get Firefox ready for them.
Attaching WIP patch which I’ve been working on with Martin Stransky. Patch also contain changes from bug #611953 (which are going to be removed in final version).
So far with this patch we are able to compile mozilla-central with GTK3, but there is still much work to do (fix exposing issues and couple of crashes)”.
I cannot follow that thread, but we will ask a Firefox developer at some point. However GTK3 porting in Firefox is in progress.