I am not sure here, but what I think joakimk is asking for is can the atmega 8 chip be used in a custom circuit.
That is, program the chip, then remove it and use it elsewhere. Such as a standalone circuit, that has no USB or serial conectivity or any of the other items that may not be needed for a particular task.
Which, as far as I can tell, there would be no problem with that.
The only issue is, there are only two ic's that can be programed right now. the 8 and the 168
However, as I understand it, the growth and excitement of the arduino platform means that this will not always be the case. Of course, I shouldn't say much as that level of stuff is way over my head.
ñ