The P-suffix "picopower" feature set is described somewhat here:
http://www.atmel.com/products/avr/picopower/Default.aspQuoting:
Quote:The key elements are:
- True 1.8V Supply Voltage
- Minimized Leakage Current
- Sleeping BOD
- Ultra Low Power 32 kHz Crystal Oscillator
- Digital Input Disable Registers
- Power Reduction Register
- Clock Gating
- Flash Sampling
I should note that the Arduino core firmware is not currently set up to utilize even the more primitive power saving modes available on the current AVR cpus, so the "picopower" aspects are not likely to be so interesting as the doubling of flash, ram, and eeprom...
None of the 28-pin picopower AVRs are showing up at (digikey, mouser, etc) and the atmel page says "by the end of 2007", so I suspect Limor's "sometime in 2008" is a good estimate, unless you're a major player...