I'd have to dig the actual ChangeLogs up, but the Kindle 3 (or at the very least a large batch of 'em) was initially released with a funky eInk driver that handled temperature changes very badly (think how an eInk screen behaves when ~0°C (i.e., *very* sluggish), except, well, not anywhere near 0°C
), and this warranted an actual mention in the "what's new" of the FW that fixed it (and it potentially made it to the CS's script before that)
.
Granted, that was a while ago, I don't recall anything of the sort since, and everything's hasn't be particularly rosy... (the PW1 lighting was generally not great, the PW2 had a few light pinholes issues, etc.).