What is an IPS display? IPS stands for In-Plane Switching. It's commonly found in high-end monitors -- gaining mainstream notoriety in Apple's displays -- and has also found its way into tablets. The iPad uses IPS displays. ASUS has an IPS display in its Transformer Prime tablet. And Samsung has its own flavor of IPS in the Galaxy Tab 10.1, which is it calls Super PLS (Plane-Line Switching).
The long and short of it is that you get better color representation -- that is, whites are white, blacks and back, reds are red, etc. -- and better viewing angles. That's perhaps less of an issue with tablets than larger displays, because you're more likely to be using it directly in front of your face. But wider viewing angles are always better than not. (And we've seen some pretty horrid tablet displays in our day.)
There's not a lot of arguing against that, technically speaking, an IPS display is just "better" than a non-IPS display. If you have the option between an IPS or non-IPS display, we'd go with the former.