I wanted to hide a few controls from the Songbird GUI and found out it's possible already, through an extension called Pane Buttons. This is how my Songbird now looks like:

These are the plugins influencing what you see above:

• ChangeFilters (from Genre-Artist-Album to Artist-Album-Title)
• iTunes (the skin/"feathers")
• Last.fm (red icon down right)
• Pane Buttons (hiding service pane and player controls)