I bet it could work in 25 mans but not too well in 10 mans. In 25 mans where there are more healers you can just act as the main healer and have twice as good heals. In 10 mans you would have to work out alot more macros and sort of do a double whack-a-mole thing with separate macros for each shaman. It's definately do-able but you would have to get together with people who don't mind a few wipes while you learn it.