Sometimes i read on the forums "cataclysm will be very nice for multiboxers", but infact i believe the opposite will be true.

5mans get a lot of movement trashs and bosses. They even add talents to allow classes to move while dealing damage. You will find a lot more group independend movement requirements in cata i believe.

I dont even think about creating a 10 account raid yet, i dont even think 5 man boxing will be as funny as it was in wotlk.

To keep it short:

- much more movement required in cataclysm
- more complicated tanking and healing mechanics

and i would believe they are going to redo /castsequence and other macro commands.