None of the existing solutions worked for me it always freezed the system. And after a freeze I could not do anything else with the integrated flash (eMMC).
So I sent the tablet back to Acer. The day I received it back I tried to flash a CM9 and it failed like the first one. Therefore I began to investigate, and finally found a solution, it needed a bit of hacking but here it is (For a 32Gb tablet) :
I made a 32gb image on my linux box, formatted it and uploaded it with fastboot.
The problem is : Fastboot won't allow the copy of a 32Gb image (way to big). Therefore I just uploaded the first 32Mb of the image and tries to repair the partition in recovery. e2fsck did a lot of fixes but finished by crashing because it was not able to write on some blocks. nonetheless It worked like a charm. CM9 booted. I'm now try to fill the sdcard with data to see if it works fine.
For those interested here is a small script for building the image on your linux box :
truncate image -s 29949427712
mke2fs -v -j -b 4096 -t ext4 image
tune2fs -O extents,uninit_bg,dir_index -C 1 image
e2fsck -fy image
dd if=image of=image_chunk bs=4096 count=8192
then in recovery (i'm using clockwork) :
fastboot flash userdata image_chunk
reboot and enjoy !
#e2fcsk -y /dev/block/mmcblk0p8