I'm not happy with rejuv change either, but...
People that are complaining about being outhealed by blue geared class x have to rethink what they are doing wrong. I don't want to sound arrogant, but use your tools people. "Work" for it, don't expect to steamroll everyone without an effort. Spec correctly, if you have mana issues, pick talents to help you last longer. NINIRVATE early, and then every time it's off cooldown. Use your OCC procs wisely. Spam lifebloom when you go to tree mode (more occ with malfurions gift). Pop a pot. Stay close to mana tide. Stuff like that. I really don't have huge mana issues atm, tho it is MORE then noticeable. I still use rejuv whenever i want - on people that need heals, or on people im anticipating thay will take damage.
As for cata, im pretty sure that at the beginning (5 man heroic gear, t11) it will be a struggle with mana efficiency (and i welcome that, i like to be challenged while healing).
"Soon" enough, with higher tier gear, mana won't be a problem, and we'll be back to business as usual. Or close enough.
There are stuff that could be easilly done to somewhat ease the mana problem, like, moving moonglow to T1 in balance tree (instead of Nature Majesty for example) etc etc.
Thing that really BUGS me tho, is that i feel that blizzard is at the strange place when it comes to druids atm. It's obvious that they don't want us to spam Rejuv like we used to, and i feel that's counter intuitive when we take in to consideration our Mastery. In order to take advantage of it, we NEED to have hots on people. Regrowth? nah. Not anymore anyway. Lifebloom? meh. On one person (tank) sure. wg? not really.
There are other issues (from my pov) like, having to spend 6 (SIX) talent points to get Efflorescence (that's also nerfed recently). If they could at least unlink it from Living Seed...
After all thease years, blizzard has come a long way (still waiting on them to fix some issues that are plaguing them from vanilla tho... like rogue vanish, pet issues fallowing them in stealth etc) and i really don't think they will leave us "broken" for long. If we're broken at all... (we'll just have to wait and see how it all plays out when everyone starts raiding in cata)
Anyways, I'm hoping they'll tweak the cost of rejuv OR do something with our mastery. OR like i already mentioned, it won't be an issue when we get our paws on good cataclysm raiding gear.
We are very versatile class, and im sure we'll adapt, like we always did. It's not the first time blizz changed the way we "tick". It's not the first time we got nerfed either.
Non the less, i'm still very much in love with my druids, and i very much plan to stick with them, no matter what. Tho i kinnda like to flirt with my priest too. ;)