In answer to your question George as to when to use a reset/supervisor chip.

In the older devices that had no watchdog I would normally use something like a DS1232 for the power on reset and watchdog. Watchdogs are good things I find especially if the device in question runs 24/7 unattended.

With some of the later devices especially Atmel with on chip eeprom they suggest having some form of low voltage detect (brown out) so writing to the eeprom when the voltage is too low won't occur. Again something like the DS1232 or microchip MCP120/130 series, maxim 802 etc are quite cheap and are always good insurance.

With some of the latest devices like the AVRs and the Aduc834 they have brown out, power up reset and watchdog all built in. I've used a aduc834 and mega128 AVR recently and they seem to be quite reliable without any r/c or external reset device. Maybe I've been sucked in by the manufacturers blurb. Time will tell.

I myself would be interested in other people's views and/or experience in this. I normally pull-apart mass produced commercial equipment (such as a PLC) to see what they do.