Fought one recently. It died plenty fast.These 4e wraiths seem like badly designed monsters to me, though. Why half damage AND regeneration? Trollish regen is unlikely enough, why do incorporeal critters get it?
They tend to have small amounts of hit points, but they take half damage from most attacks and they regenerate. To give you a comparison, the other monsters in the fight we were in had 80 to 120 hit points. The wraith had just over 40 and regeneration 5, and since we didn't have anything to bypass his incorporeality, that meant he had a functional 80 with a functional regeneration 10. His AC was middling.
We lit him on fire then curb stomped the poor guy. That shut him down pretty effectively. He ran away through some walls to heal, but we got to him before he put the fire out and beat him down.
If we'd had the right skills, he would have been even easier- there are feats and items that let you deal full damage to incorporeal creatures. That would have trashed him really fast.