I see a lot of people using it, but I don't die from it that often. It's actually a rather weak hand cannon compared to the other commonly used ones (Last Word, Hawkmoon). It's more common for me to get mopped up by a Thorn user's teammate since the poison effect prevents the shield from regenerating for a couple extra seconds. Hand cannons in general seem to be very common in the crucible, and those who are skilled with them are obviously going to perform better than those who aren't. I prefer the Hawkmoon, personally, though I only use it on close quarters maps - most games I run a scout rifle and am able to take down many a Thorn user with it.