Just some quick and dirty math tells you that the 4pc t10 resto gives you a free smart rejuv (from my experience, it's smart throughout the whole raid, so the lowest health member of the raid will get it) every 10 or so GCDs. More rough and dirty math tells me that's a 10% increase in throughput.
Some numbers from me, I use t10 4pc and Trauma:
7.6% on LK10
6.5% on BQL10
5.6% on Sind10
It would be higher if I had better reaction time. I've had some times where I'll be placing a rejuv on a target, and as I'm pressing the button I see that my 4pc procced and put it on there for me, so it's a complete waste.
But an extra ~6% healing off the GCD is still quite a lot. If you lose 220 haste, you could always gem haste to get it back to 735, and you'll see a big increase in your HPS.
EDIT: @Qieth: The two piece bonus is not amazing. You'll probably see an overall decrease in your healing if you switch out the pants, legs, and shoulders (which are all GG hot, by the way) just for 2pc.