Maybe OT but this internal temp sensor has been talked about often in the past here and at the AVR freak site. I get the impression that the real challenge is that no one has been able to come up with a good application for taking this measurement. The device's internal temperature is going to mostly be influenced by the total current draw being consumed from all the output pins used in most projects. So what usage do you might see for taking this measurement, other then maybe detecting being close to the devices maximum safe operating temperature and taking steps to deal with that?
Lefty