Not a first kill per se, but still worth noting.
It took us exactly 6 resets on the new server of Ravencrest to form a roster capable of bringing Deathwing down, this time in the proper, 25 man bracket.
We are pretty happy about this, especially taking into account the fact that we ended up with as few as 11 players moving and willing to continue raiding until Mists of Pandaria. To complicate things further, this included zero tanks.
Few weeks have passed since the kill and since then the roster only became more consistent, resulting in our first one-raid-clear of Dragon Sould heroic.
The plan for the remaining resets until Mists of Pandaria is to toy with the roster some more, score the meta achievement on the way.