Lightning/surge protection for a Arduino monitored thermistor circuit
Answer to second question:
AVRs have a BOD (Brown-out detector) whose purpose is to detect short power interruptions, and reset the controller when they occur. In the datasheets, however, you'll find this statement:  


  If the Brown-out Detector is not needed in the application, this module should be turned off.  


The reason Atmel gives is that the BOD will consume power, even during sleep. I find this odd: the BOD is a major factor in your device's reliability. If it spends long periods of time in low power modes, and a dip occurs in the power supply it may lock up and require a hardware reset. In practice unplugging it for a few seconds. Not something I would like to tell my customers.  

BTW, Atmel publishes an appnote "AVR180: External Brown-out Protection". I'm not sure what's the rationale behind this. Does it mean the on-chip BOD isn't reliable??