I had a big fashion shoot with a complex set for Eliza French couture bridal boutique on Monday in Adelaide, decided to use the 645D for the resolution and DR a medium format can provide. In the past for higher end fashion and commercial work I have used several Phase One backs and Hasselblad H2D and H3D systems. Let me just say that in one day of using it and after 400 or so shots, I felt like suing Phase One and Hassellad for making inferior products!!

OVERVIEW

1) very solidly built and weather sealed, feels just like a Pentax DSLR when you pick it up, just a bit more bulkier and heavier. But I am used to using D3s and 1D bodies so the 1.5kg body only weight is nothing to me and some others.
2) lots of great features and important functions available with a switch ie. mirror lock up for those doing landscapes etc without having to dig into menus to activate the function.
3) overall a great body that is ergonomical and feels like its worth its dollars, no creaking or plastic parts like some other MFs.

PROS

1) amazingly smooth and detailed sensor and image, great DR and retains details very well even when blown
2) for anyone who have used a Pentax DSLR before, its just like using one - menu layout and button controls all feel the same. I didnt even bother working things out as I just dived in and used it.
3) great LCD screen with a lot of colour correction and white balance controls. The 3 inch is a godsend compared to crappy LCD screens from other competitors at much much higher prices.
4) decent AF performance from AF lenses - I primarily used the new 55mm f2.8 lens for the whole shoot.
5) dual SD card slots - with dedicated card slot buttons on the camera body for quick access and control without going into the menu'
6) PRICE! Most affordable new MF camera on the market and with its functions and image quality makes Mamiya, Phase One, Leaf, Hasselblad looks like a bunch of con artists.

CONS

1) base ISO of 200 - might be a small factor for landscape ppl but you can go to 100 on Boost, albeit simulated
2) Viewfinder not as big and bright as I would like. Even the Sony A900 is brighter.
3) SD Cards - for pros like me we prefer CF cards for its speed, and its harder to lose in your pockets hehehe but the use of SD cards combined with the Raw files ranging from 60MB to 100MB for my use made it dreadfully slow to process onto the card. Shot 10 shots rapidly for one segment, that was about 1 gig worth and it took god knows how long to finish writing it.
4) slower speed for everything - this didnt apply to me - but for those who are used to using blazing fast DSLRs or even most DSLRs, the slower speed of the 645D such as changing functions, AF, shutter blackout etc may take some getting used to. Despite this, its still faster than some MF bodies I have used and would gladly use the 645D as a wedding camera even, as long as it doesnt go above ISO800 too much.

PICS (bet you are all dying to see the actual end photos right? )