I had the Pentax 645Z for about two years, but I eventually sold all the Pentax stuff (still got some decent lenses to sell) as I didn't use it enough to warrant having that amount of cash tied up in it as well as all my Canon gear. There is a photographer I see on facebook sometimes called "Forgotten Heritage" or something, he uses only Pentax gear (K1, 645Z) and his images are stunning.
I found the 645Z to be outstanding, and as others have said multiple images for HDR is a thing of the past! The dynamic range is exceptional. I've never seen an advert for Pentax cameras - I've no idea why.
So I still have all my Canon gear, but even my 1DX2 has gathered a bit of dust since I bought the Olympus OMD EM1.2 last year - and that is a fantastic little system.