The support for the onboard SiS 741GX graphics is bad. Even an old Radeon 9250 using open-source driver performs better than the SiS card with Driver "sis" set in xorg.conf.
The onboard sound does not work. The soundcard consists of a SiS 7012 controller and C-Media CMI9761A+ codec. These two chips are both supported by Linux, but ASRock have wired them in a strange way.