Symbiosis (Mastery) has been removed and replaced with Harmony. Harmony increases direct healing by an additional 10%, and casting direct healing spells grants an additional 10% bonus to periodic healing for 10 seconds. Each point of mastery increases each bonus by an additional 1.25%. Healing Touch, Nourish, Swiftmend, and the initial heal from Regrowth are considered direct healing spells for the purposes of this Mastery. All other healing from druid spells is considered periodic
So it seems that my quick reaction and probably also the fact that english isn't my first language got me on the wrong side of things. So instead of applying a buff on the target (which I thought it would do) Harmony give you a buff that increases both casts and HoT spells by X%. This ends up being a boring but decent buff to our mastery (that is changing for the second time now).
For 10 man raiding this could be a tiny nerf/buff depending on what you do. Tank healing wise this can be a buff, because the mastery gives you 10% extra on casts so you can drop Empowered Touch, and use Lifebloom's bloom more efficient. It also doesn't need you to reapply a HoT to get decent healing on casts if you would lose all your HoT on your tank for some reason, meaning that it is easier to pick up the healing again. If you intent to heal like you have been doing than this is a tiny nerf (cause the new harmony adds 1.25% per mastery, current one adds 1.45% if I'm not mistaken, so you'll get less power our of your mastery.) While raid healing this is a buff, because you don't really need one HoT to make another one more useful, because they all are as long as you cast or use Swiftmend ones every 10 seconds, which should be impossible to miss :).
In a 25 man setting this is probably works the same for tank healing as it does on 10's, for raid healing it's again easier because you don't need Wild Growth to buff Rejuv or Nourish or whatever spell you'd use after. I don't raid 25's so I can't really find anything else that could be different from 10's, besides the fact Harmony will have a lot more effect that Symbiosis would (cause Symbiosis is better for small groups).
I would also like to apologise for my quick (and faulty) post, I tend to make up my mind about stuff pretty quickly and scream blood and murder while there isn't really much to worry about. I'm still young, I'll learn... :)
On a side note I would like to thank all the people who commented showing that I was terribly wrong, however Blogger seems to had a very bugged few days and all recent comments have been deleted. Blogger promised to get all the lost comments back by the end of the weekend so fingers crossed.. I also removed the tags on this post as they were bugged as well.