Have upgraded to 4.1.B.431 firmware which is ICS 4.0.4, interesting thing though is this, as the bootloader was unlocked, I had to go through the motions of re-locking the bootloader first before PC Companion Suite would even perform the upgrade.
Sony's boot splash screen changed from Sony Ericsson with the old logo, to just 'Sony' then 'XPERIA' .... did look nice though!
Once the upgrade was complete, there was ICS 4.0.4, bit laggy in some respects, the wifi drained it like there's no tomorrow and discovered that by changing the wifi policy under Settings > Wifi > tap menu, tap Advanced , 'Keep Wifi on during sleep', set that to Never.
Overall, am not impressed with it, its definitely running on the old 2.6.32 kernel... animations are alright... I feel Sony could have done a better job on this and the kernel is crippled I would think, using kernel 3 with native adreno drivers built in - I would guess ICS would have done better!