I am one of those whoes website got hit after 21st August Google Update . My website got hit on 25th August with 40%approx drop in traffic. I searched on internet to find more about this update and found affected people talking about it on seroundtable.com/google-update-17268.html . Here I found out about the project to determine the common factors that all those affected websites have. Project Url is docs.google.com/spreadsheet/ccc?key=0AntEUErTi93DdGZzVjcydDJzd19QTl9nb0ZITXBMOHc#gid=0 (You do not need to mention ur website or ur name). So all those affected by 21 August onwards Google algo update, plz join.
My site http://www.piggysalary.com/has experienced a 15% gain in google searches since then actually.