You can read a review of it at Ars Technica - GIMP 2.6 released, one step closer to taking on Photoshop. Although some things they've said in the review has confused me:
The floating tool windows have also been adjusted so that they are always displayed over the document window and cannot be obscured. To reduce clutter and make the windows easier to manage, the floating windows will no longer be listed in the taskbar.
I don't see this at all on the Windows version. With the exception that the file menu is now on the document window, each floating window still appears in the taskbar and can be obscured. I don't see an option for it either.