My worry for a design like yours is that there is a significant lag between when power is applied and the first user instructions are executed. Especially when you're using a bootloader, isn't this interval something like 2 seconds? Doesn't that mean that the user has to push the button a long time before the processor can latch it?
@RickP,
So the basic principal of operation of your circuit is similar to that of the Pololu switch? Cool. Thanks for sharing.
Mikal