First things:
DP2 physical size and weight is basically unchanged from DP1
Startup now features a DP2 screen (looks nice)
QS button accesses two menus - 8 quick-access functions
ISO setting from 50-3200
Menu structure is revised with shooting menu accessed via button, setup menu on the top dial. Far more options presented though this may be revised in production firmware.
Performance - unable to test cards, but shot to shot time is definitely quicker, 3fps (but without a card it's hard to tell overall shooting performance and it would be unfair to judge a pre-production model). At this stage I would reckon on no massive improvements but a definite incremental upgrade over the DP1's speed.
Can't judge the lens performance yet. LCD performance looks to be the same as late DP1 firmware. Focus wheel has more resistance, very nice. Relocated zoom buttons are comfortable. QS function retains the viewfinder in background.
Image quality obviously cannot be judged at this stage, particularly with the ISO3200 setting it may be that the DP2 (and by association SD15) have had a lot of work done on the processing side.
My overall gut feeling is that the DP2 isn't going to offer any massive improvements over the DP1's general workflow and speed, but actual shooting speeds feel about 20% faster. Focus is good and the lens closest focus is around 28cm, and the wheel resistance is really perfect, something I hope they migrate to the DP1. It would make a lot of sense to my mind for the DP1 to be given an 18 month revision with the DP2's internals but retaining the 16.6mm lens.