Also, I have not noticed many other people using this item.. But ONE of the three vendors for the shards will sell you a felStone that gives you a random buff that will do either AoE damage randomly with your damage or a fire dot that stacks with your damage.

So what I have learned is that you can, get 3-4 per invasion [they each last 5mins once activated./But will only be in your bags for 30mins once purchased.]
So I pop mine as soon as Stage 3 hits, and I just clean house. My hunter crews are a force to be reckoned with. I am NOT raf linked but the xp is just ridiculous.

Also, side note. You can POP these right before taking a LFD/LFR que. Giving you an extra ability that will easily be 40% of your over all damage dealt. I was solo que'n Tank with a friend playing rogue. LFD ques, we would pop them before entering and the dps meters are along the lines of him doing 48% me doing 47% the rest divided up among the uninformed players.

Felstone : http://www.wowhead.com/item=124069

Cheers