fungus:
Timer0 generates the interrupt which increments millis(), you might need that. Timer1 normally isn't needed (it's used for PWM generation if you do analogWrite()).
Wow! Great info from all! I am not using the millis() function, so I should be good there. I just wanted to make sure the watchdog timer will still work. I use the ADC to read the temperature sensor, and I use the INTERNAL 1.1v reference voltage for that reading as well. But I should be able to turn that all off during sleep and then back on without any serious issues. The datasheet mentions a brief wait time for the internal reference voltage to start back up, so I might add a tiny delay(10) before it begins taking readings. And right now, I have it taking 100 readings and throwing out the highest 20 and lowest 20 readings before averaging. By doing that and using the internal voltage reference,I get pretty steady temperature readings.