Yea its actually very good, the only problem is the talent oints you have to sacrafice to spec into it.
its kind of like a paladin's concencrate, it helps hold mobs on u, and ups yur damage quite a bit, and more damage equals more threat, so yea its good.
Deep wounds is amazing for threat. Here's a link to a wmo for Patchwerk 10. Out of 3195 dps (7481 tps), 10.5% (339 dps and 703 tps) of that was from deep wounds. If you're looking for high tps output, spec deep wounds; it's well worth it.
I always take it. You're missing out on like a couple of points in shield spec or focused rage.
Don't forget, it procs off EVERYTHING, critical block, thunderclap and all your normal attacks etc. It is great for AoE tanking and it's nice if you like seeing loads of numbers on your screen the whole time :P