A particular reason not to use the internal EEPROM on some ADUCxxx devices would be that page erase commands will send the uC into idle mode for about 2 ms (see the datasheet). The uC will do nothing in these 2 ms, not even respond to interrupts.

For all flash-based controllers, the reset circuitry is VERY important (just search for RC reset and read the horror stories). Now, if you have a routine somewhere that erases and/or writes the flash the possibility of that routine doing something bad when the uC is "confused" during a power glitch add to the worries.

I have a product where the program flash is loaded with some customer dependent tables and I have, for the above reasons, gone so far as to a special program being used to load these tables which then is replaced by the "run" program before the product is shipped. Is that overkill? possibly, but better safe than sorry.

Can internal flash be used safely for data storage in an application, of course it can, but the possibility of a problem is so that I will only do it if I absolutely have to.

Use an external EEPROM if the 10k-up "minimum erase/program cycles" is enough or use a FRAM (Ramtron). BTW the "minimum erase/program cycles" is a concern too when using the program flash.

Erik

[edit] if your chip is one if those that have an internal EEPROM (whatever it is called) that, of course is as good[/edit]