I love this lens!!! I bought used lens in second hand market for $400, and still have 6 month warranty left. B&H list new lens for $559.
What I like most about this lens is the beautiful, classic bokeh. This lens is commonly used with Leica rangefinder cams, so now I can say my pictures have Leica-ish nuance in it. :)
I'm still struggling to use full manual mechanical lens to get a sharp focus wide open. I'm not adept at zone focusing, but perhaps the use of lens adapter affected the focus range distance. So you're not always getting focus at the stated distance.
The images produced with this lens often has creamy pastel-like colors and consistently have more grains than the 20mm Panasonic lens. But the amazing thing is you can post process the images and adjust the exposure +2EV without much degradation.
Anyway.. now I have 20 Gigabytes of raw file images in my hard drive, need to buy extra storage soon!