In general, or specifically for the E46 M3?
Some time back my father in law was complaining about some play in the steering of his E46 328i. Now on this car you can see the knuckle and coupler from within the engine bay and from what we could see, there was no play at that point. He was then thinking it could be the steering rack or tie-rod ends. It turned out to be a failed main ball joint on the left lower control arm! Never seen a ball joint fail like that, and he is so lucky that it did not fall apart while driving! Not sure why he did not spot it since he did have the car up on his ramps a number of times, maybe just never considered a problem there since he had replaced the lower control arms and bushes not too long ago at the time.
To be honest, I am not too sure to what extent these knuckle couplers wear or fail for that matter, from what I've heard in the past, they are generally pretty tough and usually components closer to the wheels wear out first...