They get a 30% cut of any app purchase. They don't get any cut from 3rd party advertisers though.

I think I've read that they're distributing part of that 30% to their partners. But Google is really making money of _every_ new internet-connected device at one point or another via AdSense.

Since Android is a defensive strategy to keep competitors from controlling the platform below Google's services, you could say that Android secured all of Googles current and future earnings. That's a lot of money.