OpenMoko Freerunner¹ is ARM-based and it runs Qtopia/QtE, GTK and E17 UI stacks. All of them are also supported on x86. GTK is Cairo-based and I heard (not sure) that it uses lots of floating-point calculations though, so ARM with GTK might not be very fast.
¹http://wiki.openmoko.org/wiki/Neo_FreeRunner
