Opera Software revealed some of the usage behind its new Opera Mini browser today. Because the software works through a proxy server run by Opera Software, it's possibly to accurately assess usage.
Opera Mini is a small Java application that brings most of the Opera Mobile experience to non-smartphones. Markup for websites is actually processed at Opera so the Java application doesn't have to do much before displaying it. This not only speeds up browsing but allows the app to run on a lot more devices.