The advantage is that in the app tray, Sony has fitted an extra column and row of icons. The dock also includes six static icons instead of four currently. We suspect that these screenshots must be from an early prototype as some app tray customisation features appear to be missing such as the ability to sort and search.
The grid to access the app tray also appears to be different and consists of a 3 x 3 grid of circles rather than the 4 x 4 grid of squares on current handsets. All will be revealed next Tuesday, so not too long to wait on official details.
Via xda-developers.
Thanks Anurag & Ben!