Depending on the program, the OP may be noticing greyscale AA. MS is using greyscale AA as opposed to ClearType in some locations in Win8 due to the fact that the OS needs to use an AA method that's suitable for rotating screens. You can't use subpixel AA on such screens since the relative subpixel arrangement changes as the screen is rotated, hence a more coarse method is used.
Anyhow, it's primarily used for Metro. However it's also used on IE10 since it and IE10M are using the same rendering engine. All other desktop applications would be using ClearType.
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