I've shot several ostriches in my time - none with trad bow though. I did however drop one with the compound a few years back. If you hit them in the right spot, like anything they'll die quickly. Generally speaking they're not that tough or hard to kill, but they tend to have a lot of fat/muscle that you can hit which will hardly slow the big bird down.
My point of reference to aim is to go straight up the leg, stop half way up the body and a little forward.
They're fun to hunt, great eating and the leather you return is superb!