Since version 1.0.1. (yesterday), the system tray icon is gone. And with it the functionality to close Spotify and remove it from the task bar while it still being active.
I feel this is a huge reduction in functionality and usability, and urge the return of the system tray icon. Minimizing the application should remove it from the task bar and put it in the system tray, so that it does not hog the limited space on the task bar.
Personally I rarely enter the Spotify main application, only to select a different playlist. It has no permanent place on my task bar.