Do you remember why you gave us the gardient back? Flat looks all cool at light backgrounds but if you have a dark background its not good to see the buttons or input filds. they are to hard to differ from the window background color. Test this at the Horde AH in OG (dark place where you have to find buttons)
Also if you change again this will maybe be the death of Missing Textures - I currently don't have time to change everything
I personaly don't care about the white button @ talent window
However if you want to change the puffy border feel free to do so for myself I already use a 1px border but thats an easy lua edit everyone can do if he wants.
+2 for stay gardient because I gave you 2 reasons ;D