There is no official way to do it through SONY's program, I think that was what Petter was getting at.
However, you can downgrade it through the use of Flashtool. It is very safe and contains minimum risk so it's up to you if you want to do it. I've personally flashed my phone a few times already and never had an issue.
These are the steps:
1)Google and download Flashtool. (Make sure its the latest version, earlier version might not support xperia S)
2)Search and download a Gingergread ftf file for the xperia S, you can find it on XDA forums very easily.
3)Once you have downloaded the file, put that file into the Firmware Folder under the Flashtool Folder.
4)Open Flashtool click on the Thunder Icon and pick Flashmode, select the Gingerbread ftf file that you have downloaded.(You should be able to see it on the right box if you moved the file correctly under the Firmware Folder according to step 3)
5) Follow on screen instruction, which should be relatively easy. (requires you to power off your phone, unplug the USB if it is plugged in, hold volume down while the phone is off and plug in the USB. Make sure you're holding down the DOWN volume button as you plug it in.)
That's all. Flash tool will handle everything and after it's done, just unplug and power on.
Good luck. and remember to goto XDA forum and look for the xperia S ftf files There is a thread there that contains ALL of the GB and ICS files there.
