One of the coolest things about Qt Embedded 4, Qtopia Core 4, is that it has support for keyboard, mouse and screen plugins. Which means easier implementation and deployment of embedded applications across different devices.
Mousedriver is usually the touchscreen, and screendriver can be an accelerated framebuffer.
Not only that, but Trolltech seperated some of the embedded gui source code. This allows for easier patching/bug fixing. Look in src/gui/embedded/ The plugins live in src/plugins/gfxdriver/ src/plugins/inputmethods/ and src/plugins/mousedrivers/. You will also see other plugins available such as decorations, styles.

In the upcoming Qtopia 4 editions, we have used this concept a bit, in the build system, to allow easier addition of device specifics and even whole source trees. More on this later.