Elsmarc - 4:08 am on Aug 7, 2012 (gmt 0)
I don't know that it will help in this, but something significant happened on one of my main sites (one which I *rarely* make any changes to related to SEO and which has been online over 10 years) on 28-29 July 2012. Search queries dropped close to 70%. I have never personally seen such a significant, almost instant drop happen before on any of my sites (yes, I have read about it happening to others). Nothing in WMT to indicate anything is wrong. I've never used link farms or done link exchanges so everything is organic.
@Tedster - I somewhat agree, but what about scenarios where you just can't really identify what you're "doing wrong" and/or "what you can do"? My personal direction is to wait and watch for at least a month. The last thing I want to to do is to start making changes without knowing what and why.