Preliminary datasheet is downloadable, engineering samples available ... press release went out yesterday ... sibling ATmega16U4, no datasheet ... "both devices will be shipping in volume in Q2 2008".
So what's the skinny here then? A real quick glance suggests that in technical terms this mostly fills out the midrange of the USB product line. The ATmega16U4 (at90usb164?) has 12 more pins than the AT90usb162, and some of those can be used for JTAG. ADC, hardware multiply, more timers, timer with 64 MHz PLL, more PWM, more USB endpoints, TWI.
We seem to be missing development boards. And the datasheet hasn't earned the USB 2.0 "certified" logo yet.
Anyone notice other goodies?