If you've been looking at those sparkling bushes scattered through Quel'Danas funny since patch 2.4 hit, be confused no longer! Those bushes are for this quest. Dear Mar'nah has discovered a new elixir here on the Isle! Bloodberries are a naturally growing plant in the wilds of Azeroth, but it seems being exposed to the Sunwell has made the ones in Quel'Danas special.
Mar'nah needs five Bloodberry samples to show you what it is that she found. This quest is hit or miss. Sometimes you can get strong circuit around the island and get the five you need in under a minute, sometimes you go batty competing with others for bushes. If there's one quest on Quel'Danas you want to do in hours other than peak time, this is it.
My recommendation is that you shouldn't pick just this one quest up and set out to do it. When you have access to this quest, progression on the island is just about over, so no need to stop and do just this quest. If you're going to do it, do it with some of the other quests. The frustration of the bushes being camped melts away if you have other things to occupy your time. Since these grow on the entire island, you can be sure you'll end up with five before you're done.
Unfortunately for you, the elixir is not as unique and she leads you to believe. The elixir, the Bloodberry Elixir, is identical to the Elixir of Mastery, adding a flat 15 to every stat. The Bloodberry Elixir can also only be used on Quel'Danas. I suppose it is good to use in Magisters' Terrace, or perhaps save for the following day's round of daily quests. Even if the potion is lackluster, the other rewards are about equal to the others. 11 gold, 99 silver, and 250 Shattered Sun Offensive reputation.
As always, if you need further information you should take a look at Wowwiki or Wowhead!