Pretty sure there is a cast bar on the throw small house sized saronite boulder action. And if you happen to be looking at your team you will notice the shadow on the ground where the boulder is heading even before he tosses it. If I notice it in time I can avoid them, but if I don't I seem to be able to spam a self cast lesser healing on eash shammy and they are back up to a good level. I have noticed if your standing next to one of the boulders when a new one hits you wont bounce very far if not at all.

If your manually targeting your team members for healing, I recommend two macro buttons for you pally shammy teams, one that specficially targets your tank and casts lesser healing wave and then targets last target, the other is a chain heal next team member and targets last target. If you have lesser healing wave on a seperate key you can set it up to self cast if no friendly is targeted. These three setups means I generally never have to manually switch targets during a fight to heal any team member. Teams with a holy priest are cake since you can just spam circle and prayer and toss the tank a renew, bubble, and mending.