Just installed it. I had to relearn a few things with respect to where those things are now located, but no biggy. My only real complaint is that when you create a duplicate layer, the new layer doesn't by default contain an Alpha channel (i.e., if you choose to do an erase through, the lower layer doesn't show through; only the background color). Not hard to add the alpha channel, but it is a pain. Maybe (hopefully) they will fix this little "feature". Otherwise, I'm glad for 2.6 since it has the potentional, via GEGL, to support higher bit color depths.
Only if you duplicate a layer that already has no alpha channel (i.e., a flattened base layer). This was not the case before, but I can live with it I guess. Still, I wish that when you duplicate a layer, the alpha channel would automajically be added as all the previous versions of GIMP did. Can't win them all I guess.