1) Download this file from RapidShare (130MB). The zip contains two files (a +110MB one and 16MB one).
2) Delete contents of db folder (C: --> Program Files --> Sony Ericsson --> Update Service --> db).
3) Run the Sony Ericsson Update Service (SEUS) to update your Xperia X10
4) Go to C: --> Program Files --> Sony Ericsson --> Update Service --> db --> 13740270 --> blob_fs.
5) Sort files by date in descending order (latest date at top). The two files at the top will be +100MB and one around 15MB.
6) Now find the two downloaded files. Rename the largest file with the same name as the top one in blob_fs. Do the same with the second. Move these downloaded files into the blob_fs folder, overwriting the original files.
7) Run the Sony Ericsson Update Service (SEUS) again.
8) Voila! Your Xperia X10 is unbranded.
Many thanks to AndyD777, xperia_man and Lollylost100 over at esato for getting this working!