Judging from my own experience and that of others on these lists this is indeed a problematic lens, and the company's (lack of) response raises broader concerns about its commitment to this market segment. I, too, had noted softness at mid-shutter speeds and documented it in a series of tests. After sending lens (and GX-1 body) with the files to the Panasonic facility in Texas, I got them back a couple of weeks later with the advice that the lens "Checks OK" and that I should use different ISOs to get sharp pictures. I have been shooting for pleasure and profit since the 1970s and owned many fine lenses that were manufactured, marketed and supported as tools, and the Lumix bodies work pretty well with them. But I am not spending any more money with the company.