I "finally" managed to power in reversed polarity a DIY circuit including an atmega328 + some components (opamp, thermopile, ds18b20). The battery pack was nearly depleted so i probably applied -3.5V to Vcc pin for 1sec. According with the specs the absolute max rating is -0.5V. For now there are no "obvious" faults with the circuit. Was i simply lucky or should i expect further, subtle problems?