Stance changes cause no global cooldown if I am not mistaken, but I did not pay attention to this. Maybe it works only because Spear Hand Strike is off the GCD, like all interrupts. It goes so fast, that the energy bar is merely displayed. This is why it took me some time to figure out, why sometimes the interrupt did not work (energy). I hit the button twice of course.
Edit:
While levelling I found Stance Dance to be quite effective, as it is not on the GCD and has no opportunity cost associated. So Jab/Clobber, Tiger Palm and Blackout Kick are 20% stronger in the Stance of the Fierce Tiger. So I switch for those into SoFT and for healing back / Chi Wave back. With some easy stance macros this works smoothly. I put them at the same position in both stance bars.
#show Clobber
/cast [stance:1] Stance of the Fierce Tiger
/cast [stance:2] Clobber
#show Chi Wave
/cast [stance:2] Stance of the Wise Serpent
/cast [stance:1] Chi Wave
I also macroed Tiger Palm, Blackout Kick, Surging Mist and Soothing Mist.
Note: Switching into Stance of the Fierce Tigers will make you lose hit gained from Spirit.
Edit2: The damage of Chi Wave is increased by 20% if one switches after the initial hit.
Combat Log Screenshot:
http://www.abload.de/img/clipboard01znjj7.jpg
Edit3: Switching back to the Stance of the Wise Serpent causes a Cooldown on abilities. If I am not mistaken it is one 1.0 and not 1.5 seconds, but this is not certain, as I may be dumb.