This enchantment will give a purple glow to the weapon.
The enchantment has 6ppm (procs per minute), and normally does 30 Shadow damage that can be resisted (partially or wholly), and even amplified (some reports have said they received up to 92 health on some mobs in Blackwing lair]. Damage inflicted is converted into healing. Rogues with Quick Recovery will not receive a healing bonus with this proc. However, the healing bonus is not reduced when the receiver is under the effect of a Mortal Strike.
Scaling lvl 60-70
At lvl 60 the lifesteal proc does 30 damage, and heals you for 30 ( if non resisted )
At lvl 61, it deals 1 less damage
At lvl 62, it deals 2 less damage.
At lvl 70, it deals 20 damage, and heals you for 20.