From our sister-site TouchArcade:
Plants vs. Zombies for iPhone and iPad both received some content loving while you were in bed last night. Plants vs. Zombies iPhone received Vasebreaker Endless mode, which packs in a total of nine levels. The iPad version, on the other hand, now supports Zen Garden, Vasebreaker Endless, "I, Zombies" mode, and four new mini-games: Slot Machine, Portal Combat, Beghouled Twist, and Zombiquarium have been included. The Plants vs. Zombies wiki has delightfully ridiculously in-depth looks on each of these modes, if you need to know exactly what you'll be getting into before updating.
The update is, of course, free for current owners of Plants vs. Zombies. The Mac version of PvZ has not been updated.