The revision is said to shrink the Xbox 360's GPU down to 65nm, reducing internal heat and power consumption. With reduced power consumption comes a redesigned power unit that only outputs 150W--one of the supposed identifying characteristics of a Jasper.
Problems stemming from internal heat are widely believed to cause the "Red Ring of Death" hardware failure that afflicts Xbox 360 owners and caused Microsoft to extend the system's warranty. The arrival of Jasper hardware has been anticipated by many, as some speculate the model will be less prone to hardware failure.
The Jasper units are believed to have entered production in August, with various Xbox-Scene posts specifying that the first Jasper systems have been the Xbox 360 Arcade model, which pack no hard drive and were made on 10-23-2008 in Lot #0843X.
Arcade versions of the Jasper units appear to pack 256MB of internal memory for game saves and downloads, going by this YouTube video and this post from Shacker sun and moon. It is not yet known if Elite and Pro models have the new internal memory too.
The last major revision of internal Xbox 360 hardware saw the addition of HDMI ports to all versions of the system last August, after the functionality debuted with the Elite.
Microsoft has not officially confirmed if the new Jasper motherboards are indeed shipping. The company has generally refused to comment on specific hardware modifications, in the past telling Shacknews that it is "constantly updating the console's more than 1700 internal components and therefore will not comment on details of specific components or manufacturing processes."