By hardware accelerating more of the operating system's graphics, Microsoft's latest should feel much snappier to use.
Once again, the focus has been on the Metro interface, although web browsing on both Metro and Desktop also get a kick along. The desktop is seemingly left in the cold in the examples given in the Building Windows 8 blog.
Text rendering should be much faster compared to Windows 7.
DirextX 11.1 is now the baseline API, while improvements in DirectWrite, geometry and JPEG/PNG/GIF rendering should speed things up, along with a change in the way DirectX redraws on-screen elements, so that things are more efficient. Direct2D effects have been brought in, so that developers have easy ways to modify an element on-screen. As the blog puts it:
Direct2D effects power some of the new user experiences in Windows 8. For example, when tapping on a tile on the Start screen, the tile uses the 3D perspective transform effect to "tilt" in the right direction. They also power the rest of our platform. For example, SVG filter effects and CSS 3D transforms are implemented using Direct2D effects.
It's unclear exactly how much this will benefit the desktop ecosystem — as usual, the talk is all about Metro. Presumably, all the APIs will still be accessible by developers, regardless of the mode that the OS operates in. We'll find out, come the October release.