This is primary to me. Avoiding aliasing buys you anything you want. Transparency per pixel and for edges must be supported. These techniques are memory and time efficient, and would be amazing for user interface. If you want proof of why this is good, capture your screen.
Transparency is important.
An alpha channel modulated by a constant will provide extraordinary opportunities for new UI innovation. Finally, gamma support is necessary to make scaling and subpixel rasterization work without visual strobing. This is relatively well supported on many accelerators today, but it needs to be more standardized. Currently, antialiased vectors can be rasterized in software using a scanline renderer as is found in Flash, or using a more traditional antialiased concave polygon rasterizer. In either of these cases, the hardware is prevented from participating in setup, transformation, or rasterization.