Two questions that come to my mind and you may be in the position to answer:
1) It seems that it matters that lens and back is aligned within 10 microns with today's sensors, how well is the ground glass in a sliding back aligned with the sensor surface?
2) How exact is the focusing mask?
The 10 microns are coming from Mark's demo of the effects of shimming and also from Joseph Holmes discussions of accuracy in the MF world.
While I've yet to get my IQ 180, the big dividing line for me is whether or not the just released live view would enable me to shoot with a tech camera without either a sliding back adapter or swapping the ground glass with the back. That is a line in the sand regarding tech camera use.
In the studio I can put my back on a Sinar camera and shoot tethered. I've tried the previous C1 live view option and found it unworkable...but in the studio I really don't care about the sliding back adapter which I use cause it works for still life images fine.
The question then becomes can the IQ 180 live view option eliminate the need for a sliding back adapter or ground glass in the field?
I don't mind using alternative methods of rough focus and framing...and I don't mind firing off a capture to "see" what I got. But, if live view as just recently released allows one to go into the field with the ability to fine tune framing and focus, then I see that as a benefit (combined with traditional viewfinders).
When shooting with the 645 camera, I don't think the live view will offer me too much. The focus mask is more useful. It's really a question of usability with tech cameras.