Our highest selling app (a hiking app) makes 15-30K/month, depending on the season. Our other navigation apps don't make quite as much yet, but some are getting there. You can figure out from my profile which it is, but I didn't want to name it in the thread and have this be something that turned up in searches.
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.
Perhaps, though it seems like a lot of these responses fall in that category.
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.