Using cycles I have simple cut out people in the scene: planes with .png textures on them. The transparency shows in the material editor and is rendered correctly but is not displayed in the viewport. This isn't a single case, I haven't seen alpha showing in the viewport since I started using blender. See screenshot:
Today I took the time to investigate because it would be really helpful to see the cut out people with alpha when finetuning their placement in the scene. I found instructions on how to enable it in BlenderRender but not in cycles. I found some related things on blender sites - even here at StackExchange - but no real answer so far... It appears that alpha should show by default when in texture/material shading modes - so what's wrong in my system?
I use windows 7, Blender 2.73, ATI Radeon HD 4300/4500 Series