http://db.mmo-champion.com/i/50260/ephemeral-snowflake/
On the PTR it's confirmed that:
Procs on HoT ticks
Procs on Overheals
That's amazing for druids. Haven't confirmed if it works for Paladins JoL yet (If anyone knows, please say!), but right now it looks that for Druids and Pallies it'll be AMAZING, if not BiS. Regardless of what drops in ICC, it's going to be very hard to replace the raw mana efficiency of this trinket.
Rejuve - 446 Mana cost - 66 mana back - 15% mana reduction
Lifebloom - 292 (effective) Mana cost - 110 mana back - 47% mana reduction (Doesn't work that way rolling a triple stack I'd assume. With a triple stack you're looking more along the lines of 20% reduction)
Regrowth - 719 Mana cost - 110 mana back - 15% mana reduction
Wild growth - 643 Mana cost - 462 Mana back (In 25 mans, It will 6 targets, 7 times) - 72% mana reduction
Is it just me, or does that seem AMAZING? If you're really hard up for mana, you can also use the 213 Rejuve trinket (I still use it on fights like Twin Valks so that I can give another healer Innervate), Rejuve gets bumped up to a 18% mana reduction as well. Right now in 25's I rarely use my own innervate and save it for other healers. With this trinket, I could lose some regen and still not have to worry about going OOM, while saving Innervate for someone else as well. The use effect might not be all that great, but the mana alone you're getting from this thing is well worth it IMO.