Meathands on 13 June 2007
http://tinyurl.com/3cfkxx
Nearly indentical to 360 on the graph with recent trending not looking so hot. A price drop would certainly bump this, but that would cost Sony a lot of money.
I can't see them instigating a price drop until it becomes obvious that MS is going to do one. At that point they might announce a drop just before MS does to make it appear in the press that MS is reacting to their actions, much like they did last generation with the pre-E3 announcment right before MS's planned E3 price cut.
