QT4.1 (4.01 had some paint engine bugs) was a nice upgrade for me.
I'm skinning my app, and 4.1 includes Alpha Blending (I'm using PNG images).. and anti aliasing. So far I'm impressed with the results. Fixed the problems I had with 3.3 and widget background origins.
How much audio does your app do? Mostly playback? Or do you use sound effects for events (button clicks, screen changes, etc)?
In relation to Xine... is it possible for Xine and your app to both send audio out, or can only 1 app send audio to oss/alsa/etc?