Nippon Ichi provides details on Disgaea 3 Return's new PlayStation Vita features in this week's Dengeki PlayStation.
The PS3 to Vita port uses the system's touch controls. You can scroll through windows with the front touch screen, and scroll and rotate maps via the rear touch panel. This should go well with the newly added overhead camera view. You'll also be able to use touch controls to toss characters around.
The game also makes use of the system's positional information capabilities. As you move around (in the real world), you'll accumlate points which can give you greater experience and Mana.
Nippon Ichi is also using the system's network capabilities. You'll have access to an "Everyone's Record" mode which allows you to view play time and damage stats from other players.