Answered both in the FAQ and the Pocket Guide. Search and read before posting.
I (combat rogue) was raiding Onyxia 25 today with my guild and managed to get my hands on a Tempered Vis'Kag the Bloodletter... so now I wonder if in your opinion this weapon is worth it. I'm upgrading from Nighttime with Liar's Tongue. I didnt manage to find any definite info on proc chances... maybe someone could help me out here?