£10k is a lot of money for a camera in anyone's book, but when you take into account that the Hasselblad H4D-40 carries an RRP of £14,634 for the body alone, it puts the relatively keen pricing of the Pentax 645D into perspective.
If you look at things from the other end of the market, the Pentax is roughly £2-3k more than the closest-resolution 35mm full-frame DSLRs - the Nikon D3x and Canon EOS 1DS MKIII - but offers a significant increase in sensor size and resolution.
Obviously, there's a difference between the way a full-frame DSLR and a medium format digital camera handles: don't expect the Pentax 645D to keep up with the Canon EOS 1D X in the speed stakes, or to match the Nikon D3S for its superb low-light performance, for instance. What you do get, however, is superior image quality - in terms of resolution - and great handling in a sophisticated yet user-friendly package.
The Pentax 645D's DSLR-inspired controls make it refreshingly quick and simple to operate, so you can concentrate on getting the very best out of that 40MP sensor.
Processing between shots can be a little slow and noise isn't quite as well controlled as it is with its cheaper full-frame DSLR peers.
If your top priority is detail in your images, you love the distinctive shallow depth of field look that a medium format sensor characteristically produces and you don't need the speedier performance or bells and whistles offered by the comparably more compact - and more affordable - full frame DSLR alternatives, then the Pentax 645D is an option that we'd certainly recommend investigating.
It is cheaper than the medium format competition, but perhaps still not quite within easy grasp of the average pro photographer. On the other hand, if only medium format will do and you can stretch your budget, it's the best value package around.