I'll make an attempt at with/without, and will agree with Aegon about jsherman's post (the words, I mean, since his pics are no longer there). I am a relative newcomer to Pentax, and a confirmed Nikon shooter. 'Dirty' Nikon shooter, if you wish.
It would be easy to just post some crappy photo for the "without" pic, but I won't do that. I'll show you a couple that I think are really strong, nice photos, but just don't have the dust. First, here's a shot done with the Micro-Nikkor 85PC, a lens of indisputable quality:
And now another Nikon shot, with the Sigma 150/2.8:
I think these are both "nice" shots, but neither really has that extra spark of interestingness, or however you want to describe pixie dust.
Now a couple of recent shots from the FA77, which I have been tripping on the past few days. The shot of the grass in particular (color obviously altered) is a perfect example of "I can just point it at anything and it looks interesting."
Now to be fair, I should post something from my Zeiss 100 Makro-Planar (Nikon mount) which I think yields the same level of "interestingness." I guess if it's not a Pentax lens, it can't be actual pixie dust, but IMO it's just as brilliant. The Zeiss 100 has long been my favorite piece of glass, but the FA77 is threatening to supplant it. The macro capability of the Zeiss (1:2) is perhaps the only thing maintaining its edge.