Mouse over macros are much better to use in Vanilla. I remember trying a really early version of healbot on classic and getting overwhelmed by the amount of spells healers use and the use of spell down ranking. If this is the case then a holy paladin, for example, will be using 9 different ranks of a single spell. Using healbot or any other mouse clicking on frames addon would mean that you would have to assign mouse clicks to 9 different ranks of Flash heal, For example, only using combinations of mouse clicks and shift/alt/ctrl. This is where mouse over macros come in .handy (shift 1 for rank 1 flash heal, shift+2 for rank 2 and so on)
Im not sure how macros work with healbot as ive never used them but I am looking forward to the challenge that healing brings in vanilla :) However, even though everyone is excited for vanilla, it was so badly designed with regards to class design/balance.