http://archlinuxarm.org/
If not familar with Arch Linux, it is a "binary distribution" with packages built from the Gentoo distribution sources.
You can get an Arch Linux LiveCD to try out on your x86{,_64} machine if curious.
http://www.archlinux.org/
Minimum kernel version is now 2.6.32 but from the looks of Freescale's git repo, they are actively maintaining 2.6.38 (although 2.6.35 is the most recent tagged as a release).
unionFS sucks (it always has to some degree), overlayFS isn't of much use before the kernel 3.x series - so auFS is the current best choice.
Will put building auFS modules for the Kindle-Kernels (KK?) on my to-do list - warning, don't hold your breath, my to-do list is very long.