I did buy a PA1000 and gave it a pretty good chance. I was spoiled by the PA4x though and didn't keep it long. I particularly like the vocal processing the 4X.
Our friend Scott Yee, after MANY years of nothing but Yamaha, bought a PA1000, and he absolutely loves it. He loved it right out of the box and as far as I know is still loving it.
The PA4x also has the MAXX e.q. system so it is really easy to set e.q. they way you like to hear it. You can certainly change and edit e.q. on the 1000 but it is far more simple on the big brother.
One good point about the 1000 is that you can play styles from the PA4X, since the 1000 is the newer model. Korg lets you go backward but not forward in using styles from the other models. You may have to change a sound or two around for them to sound best of course.
Without being too crude, the PA4X has more "balls".