I have pictures and such in my blog article on this lens: http://photographybanzai.com/2010/11/24/lens-review-pentax-da-300mm-f4-sdm/
What I like about the lens; - While I have not scientifically tested the lens; I feel that it is sharp enough from it's widest aperture and have never found an image that was was not good enough due to optical quality; - It follows the tradition of Pentax rendering with vivid contrast.
What I'm not too fond of; - Maximum aperture of f4 is challenging at times with my K-7 because I like to keep the ISO low; but I'm not sure how much having f2.8 would really help…; - The lens isn't cheap hovering around $1100; but good lenses hold value well; - Pentax SDM hasn't had the best track