To get the full details of what is new, head over to Gimp Users website for a detailed tutorial giving insights into what Gimp 2.8 has to offer.
If you want to try out Gimp 2.8, you will either have to wait for the next iteration of the Linux distribution you use, or download the Gimp source/binary from the Gimp website and compile/install it yourself.
Fedora 17 beta includes Gimp 2.8 in its repository. So you can also download a live CD of Fedora 17 beta to try out Gimp 2.8.
