When osu! is under notification area (using "Boss Key", default is [Insert] key), you'll never get notified when new highlight/PM comes in.
So I'm proposing that osu! should change its icon on notification taskbar when new highlight/PM is available, similar to Skype's notification icon (note the tiny exclamation icon):
So I'm proposing that osu! should change its icon on notification taskbar when new highlight/PM is available, similar to Skype's notification icon (note the tiny exclamation icon):