In order to get the fn keys working i first had to update the BIOS ( install windows, update bios, install ubuntu again -> a lot of fun! ) because ubuntu couldn't read the dmi data it requires to load vendor specific configurations and modules. You may check if the dmi data is accessible using the "dmidecode" tool which should return a lot of data ( see other answer ):
$ sudo dmidecode
I updated the kernel to version 3.5.3 since it has some required samsung modules compiled in to it.
I also created two keymap files and added two udev rules as described on the blog Linux And Samsung Series 9 Laptop Fn Keys. You have to replace some module specific strings ( 90X3A > 900X3C*, 90x3a > 900x3c ) as described below.
# /lib/udev/keymaps/samsung-900x3c
0x96 kbdillumup # Fn+F8 keyboard backlit up
0x97 kbdillumdown # Fn+F7 keyboard backlit down
0xD5 wlan # Fn+F12 wifi on/off
0xCE prog1 # Fn+F1 performance mode (?)
0x8D prog2 # Fn+F6 battery life extender
#/lib/udev/keymaps/force-release/samsung-900x3c
# forces key release
0xCE # Fn+F8 keyboard backlit up
0x8D # Fn+F7 keyboard backlit down
0x97 # Fn+F12 wifi on/off
0x96 # Fn+F1 performance mode (?)
0xD5 # Fn+F6 battery life extender
add this line below the other samsung related lines
# /lib/udev/rules.d/95-keymap.rules
ENV{DMI_VENDOR}=="[sS][aA][mM][sS][uU][nN][gG]*", ATTR{[dmi/id]product_name}=="900X3C*", RUN+="keymap $name samsung-900x3c"
add this line below the other samsung related lines
# /lib/udev/rules.d/95-keyboard-force-release.rules
ENV{DMI_VENDOR}=="[sS][aA][mM][sS][uU][nN][gG]*", ATTR{[dmi/id]product_name}=="900X3C*", RUN+="keyboard-force-release.sh $devpath samsung-900x3c"
The fn keys for the keyboard backlit and the screen brightness work now. The wifi and performance mode keys still don't work. You have probably to follow the instructions in the blog mentioned above.
Best Answer
Update, using Ubuntu 12.10, Kernel 3.5. My Samsung 900x3cA02 runs completely fine. Upgraded the BIOS under Win7 to P04AAC then installed Ubuntu 12.10 from USB. Out of the box things are running quite well. No problems with lid closure detection, keyboard backlight, battery status, function keys. Battery life is OK (5-6 h with wireless on, using office software, browser, thunderbird). Screen brightness can be set to very low values (15% or so) indoors.