It is possible to record 8-bit 44 ksps audio at PS16. Voice is not bad, like a cheap recorder. I wrote a library to do it, WaveRP, Google Code Archive - Long-term storage for Google Code Project Hosting..
I also did a 8-bit 100,000 sample per second logger, AnalogIsrLogger20120810.zip Google Code Archive - Long-term storage for Google Code Project Hosting.. The Arduino gets an ENOB of about 7.5 at this speed. You need a low impedance source. I did a lot of work to reduce time jitter.
MarkT,
These tests are not appropriate for dynamic ADC performance.
Here is a good article ATmega ADC tutorial | Open Music Labs.
You just can't use the AVR Arduino at high sample rates with high impedance sources. If the ADC clock is 1MHz, the sample and hold time is on the order of a microsecond.
I like to have 10 time constant, RC, periods to charge the sample and hold cap. 10 K Ohms is just too large.
Calibration would change with temperature since gain and offset change.
Integral Nonlinearity is usually less dependent on temperature.
Atmel doesn't publish much about the properties of the AVR ADC so you can't be sure without tests. Doing tests of ADC properties as a function of temperature for the AVR ADC would be a pain.
The Arduino ADC is not bad for most hobby use with low impedance sources.