I think that Atmel uses an unorthodox way of IO circiuitry to detect the Bootloader state. I used a PNP transistor that draws the PSEN low. When the power supply is only 5V, this PNP draws the PSEN to about 0.9V then the bootloader will not start. I had to increase the VCC to >6V, the PNP rises then up to 1.8V, drawing >60mA but then the Bootloader starts. Taking the PSEN down with a N Channel MOSfet works alright with 5V..

I also observed, that newer parts seem to have less current consumption.

I don't think the chip will suffer, but it gets warm. I was a little worried about it, so in another project, I use a pushbutton to short PSEN to GND only during startup.

Werner