Some suggestions about themes:
1. Knob rings are really helpful. It would be nice to have them for the Mercury theme as well.
2. Some parts of the UI are not affected by the theme:
- several scrollbars are Windows style, not Sonar style
- the left/right arrows for tabs in the docking area
3. While I like the dark colors of the Tungsten theme, I won't use it because of the flat buttons. For a user interface that has so much visual information like many areas of Sonar (e.g. the mixer), it is really helpful to have 3D style controllers for everything where the user can interact. For good reason, the Tungsten theme still uses 3D for faders and knobs. So, I hope future themes will have 3D buttons.