Its not 'petrify flesh' that keeps you from flying. That spell is 'Calcify'. Calcify gives I think some additional damage reduction at the cost of being unable to fly. Petrify flesh reduces your moves every tick but it also I believe either provides some slight DR or maybe resitance to some types of attacks, im unsure which.

Im pretty sure you can't cast calcify on another person. Doesnt matter though because transmuters get earthbind.

Petrify flesh is situaionally very potent especially in conjunction w/ accelerate on folks who don't hit that hard or that often. The speed that you lose movement when fighting while accelrated and petrified is frightening. Great spells to use in cabal defense at the inners.