I've done it. My app has had about 3000 installs now, with 500 or so regular users, being live for about 3 months. The ad money isn't great, although it could be because the majority of my users are in developing countries, so if your target market is the US you should do better. My total income after paying for my server is probably only $20 a month, pretty sad! The app is growing though, so it'll hopefully increase over time.
I rationalize all the time spent (about 3 months worth of evenings) in two ways, firstly I wanted the app for myself and use it as a vehicle tracker, saving me about $10 over the cheapest vehicle tracking in my country, and then if I add to that my current monthly income and multiply by 300 (25 x annual) it means this app is worth $9000 to me. In my view that was well worth the 3 months of evenings. Plus income should hopefully grow and not shrink, even if it only grows slowly.
If you're interested, here's the URL:
http://gpstrackerforandroid.com/