Well I just pent a few hours with my K-5 and the LensPen SensorKlear… probably because I just normally don't do this at all, didn't realize that the Y axis on the image and sensor are flipped until later and my LensPen isn't brand new- I have used it to clean some small lenses so that probably didn't help.
MY GOD what a task. Hope that I didn't scratch it or anything (doesn't seem like it, I get a hunch its not that easy to scratch the surface as one may think, but still). After a few hours I finally was able to clean it except for a very tiny faded out spot that shows at F11 and super dim.
I decided that point, well that was good enough.
I really think Pentax has probably evolved their anti-duster to the point it's somewhat useful, but Olympus is still the gold standard. That said I did find dust in my 620 when I did the small aperture test, it just normally doesn't show up. On my E-3 also (when I had it and did the test). So it works good aided probably by how normally not shooting in 4/3rds are closed apertures tends to also hide it.