I just finished reading Nick Devlin's early review of the Pentax 645D over at Luminous Landscape. It's worth a read, if you're interested in a $10,000 medium format digital SLR.
Nick points out that the 645D inherits some of the modern DSLR handling characteristics from the Pentax K-7/K-5. I think I've read similar statements over on the Pentax forums. But I noticed, from the pictures accompanying the review, that the top panel is also a bit reminiscent of the legendary Pentax MZ-S, with it's slanted control panel.