Qt 5's base functionality runs on the N9 out of the box. Qt builds with full OpenGL ES 2 support. Sensors, multimedia and additional modules will almost certainly require additional work if you intend to use this functionality. You are going to be using the XCB backend which replaces the legacy xlib backend implicitly used in the Qt 4 series.
Caveats (Warning? Achtung Ulv!)
Overriding system libraries on your N9 will result in tragedy. You have been warned, and although your should be able to avert disaster. If you misstep you might need to cold flash your device.
- Qt Creator Harmattan support
Harmattan Platform SDK for xcb (or swipe it from the webkit dudes .deb packages)
The xcb libraries are not shipped as part of the standard Harmattan SDK. You can get these via installing the platform SDK and using apt within scratchbox to install the required packages. The missing libraries include:
libxcb-atom.so libxcb-event.so libxcb-icccm.so libxcb-image.so libxcb-keysyms.so libxcb-property.so libxcb-sync.so libxcb-xfixes.so
The N9 requires a hardfp toolchain. The Harmattan toolchain shipped with the Nokia Qt SDK suffices, and just needs to be explicitly passed as an additional compiler argument.
./configure -release -make libs -prefix /opt/dev/qt-qpa-5-harmattan -device linux-harmattan-g++ -device-option CROSS_COMPILE=<sdk_path>/Madde/toolchains/arm-2009q3-67-arm-none-linux-gnueabi-x86_64-unknown-linux-gnu/arm-2009q3-67/bin/arm-none-linux-gnueabi- -sysroot /scratchbox/users/<user>/targets/HARMATTAN_ARMEL
Qt Labs posting 
- Qt Webkit teams documentation