johnhh - 8:13 pm on Oct 25, 2011 (gmt 0)
I would take this as eliminating this factor from any traffic drop, whilst a manual review may score you down on other factors, or the algo itself may be doing it, at least it eliminates a number of posiibilities.
a manual spam action
I understand other replies say other things, for example, you are a "doorway page". Other examples can be seen on the, rather agressive, google forums.