For those living along the path of the recent Derecho that travelled from Chicago to the area of Washington, DC, you will no doubt find this an interesting resource:
This is an excellent summary of not only what a Derecho is, but how it manifested itself on 29 June 2012!
For those that didn't experience this line of storms -- it was easy to notice the power of the gust of wind ahead of the line, with hurricane strength gusts. It was quite impressive, indeed. The official wind-gust at Dulles International Airport (IAD) was 71 mph.
Just a taste, note this splendid radar sequence:
Radar Mosaic of the 29 June 2012 Derecho. Keep an eye on Chicago, Illinois. It is at that point that the line of storms turns SE and charges to the Mid-Atlantic!