Dean Takahashi has news up on his blog
that Microsoft is about to make the change over to newer, smaller chips for the Xbox 360. The newer chips would be around 30% smaller (65 nanometer vs 90 nanometer) as the original Xbox 360 chips which would dramatically decrease the cost of the chip (more chips per fab) as well as lowering the heat generation and energy consumption of the chips. Microsoft could pass this cost savings on to consumers in the form of a price cut this week which is more likely now that Sony has trimmed
$100 off the price of the PS3. We won't have to wait long as any price cut will be announced tomorrow night at their E3 press conference.
Update (Chuck) - Fixed an error with the size of the processor)