We've had a lot of talk about the set bonus in varying places already. See thread: Healing 4p T11 (it won't let me link the thread).
The set bonus isn't terrible for disc by any means. The biggest issue I have with it is that one spec has the buff constantly, the other has to manage 2 spells every 10 seconds to get it. That's a lot of micro-managing and forcing us to use spells at specific times when another tool might have been a better choice. I'll still be getting my 4 piece and just praying that they bring it more in line with holy. Having it proc off Penance and giving a 12-15 (maybe even 20!?) second buff would be a good fix.
As for the int vs spirit, well I would rather have spirit procs and get static intellect elsewhere, although if they were thinking about changing it to int, I think they would have to make the bonus 400 int to keep it in line with holy, since we get so much from int.