I wondered if they switched from the 90nm to the 65nm processor chips to run cooler. I read somewhere that the new 80G may not support all PS2 games. I think it is because it uses more software emulation versus hardware emulation for backwards compatability. I don't know if this lack of compatibility is related to the possible use of 65nm chips or not.

In either respect, I am wondering if the 80gb is quieter than the 60gb?

IBM started manufacturing the 65nm cell processors but currently they are used in cell blade servers, there hasn't been an official announcement about using them in the PS3. About fan noise I'd expect them to be similar, there has been a few posts in forums that the 80gb is quieter but no technical report of this kind anywhere, if there were an actual difference we would have known by know imo. Also, the ps2 compatibility is because the 60gb version has an additional chip inside called the emotion engine (EE) this one was removed in the 80gb and now using software emulation.