According to a recent IGN podcast, Nintendo is having problems in development of Wii MotionPlus. "Hiccups" need fixing.
Kotaku points out that the "Spring 2009" release for Wii Sports Resort has been quietly adjusted to just "2009." But with a few different companies bragging about their MotionPlus functionality for games hitting around June, coupled with the pretty extensive hands-on with the peripheral we were allowed almost a year ago, it's hard to believe that technical glitches could be all that devastating at this point in time.
If anything, it seems like IGN is confirming what we already suspected after Nintendo kept so quiet since E3. Wii MotionPlus was delayed. Now it's on schedule for a June-ish release.