Anyone who is considering downsizing to a mirrorless camera should read DivePhotoGuide's review of the NEX-5 http://www.divephotoguide.com/underwater-p...er-photography/
Their conclusion:
"Even at first glance, it is clear that the NEX-5 is not for SLR shooters looking to shave some excess weight off their overall kit while maintaining the same quality camera. The limited buttons, lack of lenses, and slight shutter lag will cause frustration to any experienced SLR owner"