I found that test to be quite interesting. So, basically, if you fully cycle a tank to, say, 2ppm once every 24 hours it's likely that the tank can actually handle a level much higher than that. And nitrate needs to be insanely high (much over 100ppm) to actually crash the cycle.
Now, my question is how high must nitrite be to crash a cycle?
I guess I'll continue advising people that water changes won't hurt, but that their cycle is probably a little more stable than they think it is. It is quite amazing what our filters can do.