NOT 384MB ram, It is 256MB!
I have got the xperia but I was just as you confused about whether the it had got 256 or 384mb ram, so I decided to call the special x1 support to get my question solved.
The guy seemed very educated on the phone, as he answered my question without hesitation.
Apparently that guy who said there were going to be 384mb ram, was wrong. It IS 256mb. I was told that he had mixed up internal memory and RAM.
This was really dissapointing to hear as I cannot get how a senior product manager can repetetly make the same miss saying over and over again without ever publicly say that this was a miss saying.
None the less, I am keeping my phone. Its great still.