After reading about some of the great MF Pentax lenses available for decent prices(in Photo Trader) I started searching out for more into on these 645 series Pentax cameras a few years ago too.
The only concern I had for the 645 series was the serious mirror slap problem it had, where mirror lockup was essential in many cases.
Looks to be a great system, as long as the price is right.
Considering Pentax's current DSLR pricing, if this MF system comes in at high end DSLR prices(eg D3s 1Ds MkIV levels), it'd make for a compelling alternative