Taken from IGN:

For Pikmin, the new feature mentioned in Famitsu concerns saving. When you save, the game stores day-by-day records of your play. You’re free to restart play from the day of your choice.

For Mario Power Tennis, Nintendo has made the game fully Wiimote compatible. You can now swing the Wiimote like a tennis racket to control your swings, performing forehands, backhands, tosses and smashes by swinging the Wiimote as you would a normal racket. For spin shots, you simply change the angle of the Wiimote when swinging. To perform special shots, you press buttons during the swing.

Mario Power Tennis will support play both through the Wiimote on its own and through a Wiimote/Nunchuck combo, the latter presumably allowing you to control your characters on the court.