If you can do ADB into your nook (i.e. using adbWireless):
adb connect <nook-ip-address>
adb push uImage /media
mount -t vfat /dev/block/mmcblk0p1 /media/boot
cp /media/uImage /media/boot
The quality of the zoom depends on the program you are using (I use ezpdf, which shows always great results) and the quality of the pdf file you use. If it was printed with lower resolution (100 dpi or less), it won't look good even on a 10" tablet.
Files from my MBA or the ones that I scan myself (using at least 200 dpi) always look pretty sharp.
Sorry I realized I posted this on the wrong thread.
I was refering to NoRefresh. This makes the screen 1-bit and then things look really bad, even documents with "infinite" resolution due to vector format, e.g. documents originating from (La)TeX (which are most of the documents I use).
Of course this is not the fault of multitouch, but only of NoRefresh.