I had very annoying problem with UX32VD which eventually led to me returning it -- it has broken thermal setup or something. It combines two factors:
1) When you're using the computer for light tasks (but not when it's completely idle), the CPU will warm up to about 55 degrees C. That's not bad temperature for CPU, but the problem is that the fan is set up to start at 50 degrees C.
2) The firmware is broken, and due to bad feedback loop or something, refuses to run the fan at any other setting than zero or full.
This means, that whenever you do anything with the computer, it warms up to 55 degrees, then it starts the fan, then it cools down and stops the fan, then it warms up ... web browsing on my UX32VD was like this: WHEEEEEEEEEE UUUUUU <ten seconds of silence> WHEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE <fifteen seconds of silence> WEEEEEEEEEE <five seconds of silence>, ad infinitum.
ASUS knows about the bug, but won't fix it. Now, some units don't have this problem, or start experiencing it after some time, but ASUS won't do anything about that, because "all computers run fans sometimes, right?". So unless you really need that RAM, I would stick to UX31A, because according to forums, about every UX32VD has this problem, but only some UX31A do, probably because of the dGPU.
Of course, ASUS promised updated version with Haswell, that should have 8 GB RAM by standard, but know know when that will arrive. Also, there was loss of display quality from Zenbook to Zenbook Touch, and thanks to Intel, every ultrabook will be touch now, so if you like that screen, you might be better of with UX31A.