The new Unity 4.6 comes with a new GUI, when I change de resolution on Unity the UI Button scales perfectly but when I test on the Nexus 7 device the Button looks too small. Any
If you want the button to be the same size for all screens and resolutions, you have to add the canvas scaler component to the canvas and the set the screen match mode to: match width or height, here is the link to the docs, this helps a lot if you want to aim to different sizes or resolutions:
http://docs.unity3d.com/Manual/HOWTO-UIMultiResolution.html