Jesus, maybe you can make a "microcontroller" work on a bread board, if you don't have any digital signals routed outside of microcontroller. But even then the power supply decoupling isn't adequate. But if you talk about "microcontroller systems", where a lot of digital stuff is connected to your microcontroller, then, dear Jesus, I must tell you, that a bread board design is entirely unsuited! It's the total lack of solid ground plane that matters. Today our digital boards must fullfill very restrictive standards, referring to emitted radiation for instance. And a complex digital microcontroller circuit on a bread board without solid ground plane will most heavily violate these standards!

Kai