What originally interested me the most in Qt 4.6 was its native graphics backend (X11/Xvideo) as opposed to raster backend in Qt 4.5. However, I don't know and haven't checked whether Diablo's X server has Xvideo extensions. Apart from graphics backend, Qt 4.7 has WebKit with tiled backing store and greatly improved animation framework.

Also, it's nice to be able to use the same version of Qt for both desktop and N810. This allows me to work on an application on desktop and only occasionally compile it in Scratchbox to see how it performs on N810. Currently it's too easy to use features that are only available in Qt >= 4.6.