The difference is that qemu is an emulation software, while Ravello are using full (nested) virtualization, so there's hardware acceleration here. You can see some more details on how to run it there at http://www.ravellosystems.com/blog/android-emulator-on-amazo... .

I thought android emulator performance was not good because of qemu.. how is this different??

I wonder what is this good for? Why not just running it locally or on a device?

I think it can work well for Android app continuous integration. If you can spin up multiple Android emulators in the cloud, you could test every build against a plethora of Android devices and accelerate your development.