Unlike the early edition of the app, it now works on Android 1.5 devices. In fact there seem to be two different versions of the app - one for 1.5 devices, and one for 1.6+ devices. It's not immediately clear what the difference is between the two, so if you know then do enlighten us in the comments below.
In our brief testing, we found browsing and finding music to be very simple. To buy, you just put in your email address and password and then it'll check off the login, authentication, purchasing steps in front of your eyes. Tracks will download over both Wi-Fi and 3G networks, though after download they just sit in a list. You can't just play them by tapping them, you need to open a separate media player app.
The Amazon MP3 application for Android is available for download now in the UK and it's free. Just search in the Android App Market for "amazon mp3" and you should find it. Most tracks cost 69p, and can be moved around whatever devices you like by hooking up a USB cable to your phone.