Yep, new major GIMP release has been taken out of the development branch and become a stable release. It's a big jump from GIMP 2.4.x in which it behaves more like a professionals tools with no floating toolbar anymore. It's not just the UI who get revamped, but also in the inner side of the process as well. GIMP 2.6 has integrated GEGL, the graph based image processing library that will eventually bring high bit-depth and non-destructive editing to GIMP and also moved some 2D graphics processing to Cairo (see the comparison).
There are lots of new things on the GIMP 2.6 which are interesting and i can't list them all here. Curious? Just go straight to the Release Notes of GIMP 2.6