I use RevMob on my apps. Like Tom already stated you might not get 10% clickthroughs and you certainly will not get $1 per download.
When your app stays too long without generating any download, when it does, then you might get $1 or even more. But if you have regular downloads you will most likely get a couple dimes.
Also, you will get some revenue (very low) from a high amount of banner "printings" even if they don't generate any clicks or downloads.