[nzp]

As a non-native speaker I agree with this. But I've noticed something interesting: before I was aware that mixing up the two was common with native speakers it would never happen in my own writing, but once I realized people do make this mistake I became susceptible to making it too. I still don't, but now I sometimes have to make a conscious effort to differentiate the two. It's amazing where social learning can show it's effects. (And BTW, I think I would just kill myself if I ever mixed up affect and effect, I see that a lot, and for some reason it annoys the hell out of me.)