just flash back the original firmware using pc companion I recall
maybe need those more experience to advice u
hahha in not into rooting
If the update kills rooting, it'll get rid of the Superuser option available brought by rooting
Worse comes to worst, download the original .ftf file for the firmware of your handset and flash it using flashtool
Customizing and kernelizing the Xperia series is pretty foolproof by now, just follow the written instructions and you'll be fine =)
Even my arc S is running ICS Beta with all the G-apps, Wifi and BT enabled now, perfectly stable and smooth with its UI running on the GPU. Bloody smooth compared to any GB phones out there, even the XS, with a Live Wallpaper in the BG
Note that rooting does not kill your warranty, and unrooting is easy as well for the Xperia series
Unlocking the bootloader for your Xperia phone however, is a different story altogether
I'll go get in trouble with my bosses now, TYVM! =D
I tried to order via rakuten, stuck at the 3rd part where i was asked to make payment. 
