i kept ps11 on my desktop and have ps 12 on my labtop, the biggest differance that i se is in render 11 has a lot more options on lighting your pictures that ps 12 does.
i am no expert, thias is just what i see diff,
i am no master of ps11 on my desktop and ps12 on my labtop, witch replaced ps9 on my labtop. the one big differance i saw bwtween 11 and 12 is in 'render" ps 12 is limited on light evfects on ps11 under "render" you can do ALOT with lighting effects with your pics.