An issue that came to my attention only recently is that the borders of WPF (update: WPF is not actually to blame) windows without captions/title-bars (that is, with ResizeMode set to ‘CanResize’ and WindowStyle set to ‘None’) are drawn incorrectly when the DWM (read: Aero Glass) is enabled. Specifically, the upper and left borders are drawn one pixel too thin (e.g. 3 pixels when the system setting is 4 pixels) and the colour of the bottom and right borders is different to that of other windows. I’ve tried to illustrate these differences in the screenshot below (the image on the left is of a WPF window).
It is conceivable that this will be fixed in a future version of WPF Windows, but for now we can use the DwmExtendFrameIntoClientArea function to do it manually. This is only necessary when the DWM is enabled, of course.