Simple question: can Quickly use GTK2 only or also GTK3 for GUI?
As of 12.04
Extended answer: Since all the code produced by quickly can be edited, you can change it to support gtk3, but it does not come with support.
There is however a branch of quickly in development that (only) supports gtk3. You can see the difference in the templates: some have
You should be able to uninstall your current quickly version and get the gtk3-enabled version with:
I have however not tried it and it is of course not the current stable version of quickly (which has lots of implications...)
Ubuntu 11.10 uses Gnome3/GTK3 by default, as well as Unity, so yes, it supports GTK3 :)
I see that you've added a pygtk tag to your question. You should consider dropping it in favor of GObject Introspection, as g-i and PyGTK are not compatible anymore. It's an easy transition though, and g-i provides many other tools as well. PyGTK is not going to be developed any more either, so sooner or later, you are going to have to make the switch. There will never be a GTK3 version of PyGTK.