I have had a problem with font rendering on Windows 8 Pro RTM, Release Preview and all previous iterations of Windows 8.
I am able to get reasonably clear fonts only in Firefox and Waterfox by setting in about:config gfx.direct2d.disabled = true
Apparently the font rendering in Windows 8 is different to Windows 7. One aspect is the use of grey-scale anti-aliasing instead of RGB anti-aliasing.
On a Mozilla forum one poster had noted this problem on PCs with varying configurations including Intel HD graphics and both Nvidia and AMD video cards. I also have recently updated my hardware and the font problem persists, so it is not the hardware.
I am dual booting Windows 7 on the same PC and have no font problems whatsoever in Windows 7.
The worst font rendering is in IE10 (desktop version). Disabling hardware acceleration in Internet options > Advanced makes no difference.
Parts of Office 2013 are also really bad, such as Word.
The blurry fonts make Windows 8 virtually unusable for me.