One of the many interesting things covered in coverage of this years GUADEC was GNOME Builder — an IDE that will focus purely on GNOME applications, with a goal of making it “Dead Simple”. covers the content of post about day 4 at GUADECChristian Hergert’s talk about Builder (including him announcing the brave step of quitting his day job to work on it). While there are other IDEs in Fedora (like Adjuta and Eclipse) that can be used for development on the GTK+GNOME stack, none of these are focused purely on development of this type.
A quick look at the mockups for GNOME Builder show that this IDE appears to be following the GNOME3 HIG fairly closely, with a fairly minimal interface. However, the plans for the IDE do include a wide range of features that will make the creation of GNOME-centric applications a lot easier to develop. Such features include: integration with the built-in GNOME DevHelp, the ability to easily add DBus and Gsettings into applications, git integration, and the ability to debug and profile your application with Perfkit and Nemiver.
There is also a prototype version of GNOME Builder available on github if you want to try to build it and see how the early prototypes of this tool are looking.