My son and I just completed his science project which involved LEGO and PF motors. Our exploration was called "Can you train a chicken?"
To answer this we created the "chicken box" that you can see in the YouTube clip. We spent a couple of days getting the chickens to associate the beep of the box (a little piezo wired onto a PF connector) with being fed their favorite thing; string cheese.
My son would lead the chickens to the box by showing them the string cheese. At the same time he was triggering the beep and opening the box (via the PF RF remote). After that he'd put the cheese in the box and the chickens would chow down. I'd say the one unexpected design challenge was the fact that the PF motors turned so FAST! I ended up making a tiny gear box with a couple of reductions in it. This made the action slow enough as to be usable (and not threaten the chickens).
Then every morning and afternoon (before letting the chickens out of their run) we'd load the box with cheese. Peaking from a window, my son would trigger the beep and the chickens would come running to the box. He'd open the door and they'd chow down. At the end of seven days of experimenting, we aren't sure the chickens came running because of the beep or because of the sound of the PF motor (or both), but it became obvious to us that they knew the beep meant the box was going to open and provide them cheese and that was enough for us for this first experiment.
I'm contemplating another experiment that requires the chicken to tap a specific sequence of touch sensors to get food (this is similar to chicken training I've researched on the web). In that case I WILL use the NXT and let you know how it goes.