Well I really think it depends on your level of comfort and how real you want to be in your training.
For instance, when I first started to train catching bullets in my teeth, we used BB guns. But I soon realized the velocity difference was really screwing with my timing and if they day ever came when I had to catch a bullet on the street, I'd be screwed.
Same goes for arrows or spears, anything but a live bladed tip throws off the trajectory and speed, and let me tell you, if your timing is off catching an arrow in flight, it's a bummer.
Seriously though, unless you work for a traveling circus throwing knives at pretty girls, live blade work is both dangerous and counter productive.
** disclaimer** those of you who work with Swords might have good reason to use live blades, don't know never trained in weapons.
Undefeated in all of Asia!