According to IGN, Nintendo will have to delay the planned June release of Wii MotionPlus in order to solve a few problems with the Wii Remote add-on.
During IGN's Wii podcast it was noted that "Nintendo is internally struggling with Wii MotionPlus, trying to figure out a few hiccups". These problems would see the peripheral and attached Wii Sports Resort delayed.
Nintendo's remained tight-lipped over the rumoured delay. If accurate, the later than planned Wii MotionPlus release could also impact titles from third-parties looking to capitalise on the new functionality offered by the add-on - EA's Grand Slam Tennis is one such title.