I wouldn't call it totally passive, but if we ignored it, it wouldn't stop making money. We have consistently grown the sales over the last couple of years, and we are about to introduce a premium in-app purchase.
I have always thought making iPhone apps was a good business, despite what you hear on this forum.
I'll say this - I used to work on this app day and night, and now I try and just do the part I enjoy the most, and leave most of it to expert developers and friendly support people. My focus is now on growing the platform, business development, and design work.
How do you get 'outdoor maps' into the App, ie do you license them or are they available freely somewhere?