Based on this... http://www.atmel.com/images/doc2508.pdf ...if the resistors are large enough, the processor will not be damaged. I assume that, when the voltage is above 3.3, the clamping diodes on A0 and D2 would conduct thus defeating the intent.
Does the voltage divider have that much of an effect? Is a few milliampere drain going to cause a problem?
Based on your link, it appears I could just bring the battery plus side to the analog pin directly through a current limiting resistor and read the voltage. It will read 255 (or whatever the max value for 10-bit resolution is) until the voltage falls below 3.3V. The internal clamping diodes will protect the pin as long as I supply enough current limiting to it. Is this right?