GIMP 2.8 is largely being held up by the new user-interface and broken graphic tablets support, or at least that was the explanation back in January. In mid-April we now finally have the release of GIMP 2.7.2.
This new development milestone has the new single window mode user-interface, an all-new brush engine, layer groups, and text-on-canvas support. The cage transform tool developed as part of a previous Google Summer of Code was finally merged, RTL text support is improved, many changes to the input device handling code (some of it being merged from their GTK3-port branch), various memory leak plugs, and many other development changes.
The GIMP 2.7.2 release can be downloaded at GIMP.org. Sadly it looks like it will still be a while before GIMP 2.8 finally surfaces. Once it does, succeeding GIMP 2.8 will be a version that really focuses upon using their GEGL core (the Generic Graphics Library) that has been in-development for years now.
More information on the GIMP 2.7 series can be found on this release notes page.