On page 107 of the main book it states, under Ready a Weapon:

A character can ready a number of small throwing weapons, such as throwing knives or shuriken, equal to one half his Quickness (round down) per Ready Weapon action.

A friend of mine is playing a "ninja" type physical adept and figures that because the weapons are ready he can throw three shurikens, his Quickness is 6, in one action.

He has the physical adept powers of Quickdraw and Missle Mastery.

Is that right, or is he limited to one shuriken per simple action?

Not quite.

Quick Draw allows you to Ready a Weapon without wasting any actions on it if he makes a successful Reaction (4) Test. So yes, he can ready three of his shuriken in no time. However, it still takes a Simple Action to throw a single weapon so he can only throw two of them in one Combat Phase (and, thanks to Quick Draw, he will still have a Free Action available to do something else). Once he runs out of readied shuriken, he'll have to make another Quick Draw test to read three more.

A normal character would have to spend a Simple Action to ready three shuriken and then one Simple Action to throw each of them. So this ninja character is gaining a nice advantage with his investment in Quick Draw.

As far as Missle Mastery is concerned, it has no impact on any of this. The only thing it provides is a +2 Power bonus with the shuriken.

For the whole debate.

Actually reading the whole debate (thanks for the link) I noticed something. The action to quick draw is a simple action. By expending a quick draw action, you use a simple action to draw and fire a pistol. It does not allow you to ready a weapon for free. You have to immediately use it. Expending a ready weapon action is also a simple action. It allows you to ready a firearm or half your quickness round down of throwing objects. These actions are different and not necesarily compatible. The debate included an example of throwing knives sheathed at your hip. This was a perfect example of what the adpet power of quick draw is. You draw and use a weapon as a simple action. You can't combine the rules for adept quick draw (or regular quick draw) with the action of readying a weapon.

I prefer pointing people to this thread, chielfy because it involves juggling and destroying a car.

So, as my first post here, I would like to say that characters I've had and those of other players that have used throwing knives/shuriken for anything other than a distraction or chemical delivery system have found them worthless (though very cool ).

When we play, we [House Rule] usually give ninja characters like yours the ability to throw his quickness/2 shuriken per simple action, and treat it like a burst for damage. They also have to have the same target. Again, this is just our house rule, for making it cooler to use them.

I personally like them as good signature item for a non-lethal character: I don't like having knives (even small ones) thrown into me, and would be less likely to pursue somebody and more concerned with stopping the bleeding.