If ATI drivers are rubbish I'm sure Steam coming to linux will make some changes in AMD's thinking.
Also waiting for a less messy multimedia and audio api is nonsense. Because we might never have one. The best thing to do is to use what we have to its limits. I'm not sure why STEAM would need multimedia apis (or what is a multimedia api? it seems too vague) but for video we have gstreamer which is a freedesktop standard and it has a clean codebase. For audio we have PulseAudio which seems to work ok for a while now.