A search on the forum didn't reveal any results on the terms, so perhaps I'm the first one here to say this??
I want a K-01 because it will allow me to use the incredible Pentax lenses, both current and legacy, with a phenomenal and proven sensor.
And I can use them silently. Zero shutter sound. And with full-time live view I can shoot more discreetly than I can with a viewfinder at my eye. And it's the best compromise I've ever encountered as a backup camera that doesn't take up much space in the bag.
To put this in perspective, one of my backups is a Canon G10. It works, particularly in good light, and it's my only halfway decent silent option at this point, but it's nowhere near the quality of a proper SLR. And according to camerasize.com (using the Canon G12, the closest match they have in their system) the K-01 is just 8% wider, 4% taller, and 22% thicker than my G10. (Okay, I looked up the dimensions of the G10 and did the math myself. The K-01 is just 12% wider, 1% taller, and 26% thicker than the G10. In other words it's 43% larger overall.) Not much of a size penalty considering the tremendous increase in quality and even larger increase in functionality with interchangeable lenses.
Is it perfect for every situation? No. Is it the sexiest industrial design ever? Not even close. Will it be my only body? Not a chance. Will it be in my bag? You bet.