GTX 560 monitors
GTX 970 rendering
Broken: 2.74 Official 64bit
Short description of error
Transparency does not work in material view. The only way I found to make it work is to switch to Blender Game renderer and change the parameter Alpha Blend from Opaque to Alpha Blend and than switch back to Cycles renderer. The problem is that the object behind the transparent object are not visible unless the object is selected with RMB. See the attached blend:
Exact steps for others to reproduce the error
Open the Blend file - you can see through the monkey and whole cube is visible.
Deselect all (A) - you can see through the monkey bet the cube behind the monkey is invisible.