http://www.gimpusers.com/news/00420-...nally-released
I used to use GIMP, but when I started trying to process astro-images I realised how important 16 bit editing was and switched to PhotoShop.
So I guess the most important new feature of GIMP 2.8 is that it finally has 16 bit support! There are many other new features. Check out the link above and the GIMP site:
http://www.gimp.org/