>- It will accept UP TO 512mb SD cards (stated on the box/website)
I, as well as others have played MP3s off a 1GB SD card, so 512MB is not set in stone.
>- Playing Video Files from the SD card is still a pipe dream
Yep, the built-in video software can't play off SD card, and no one has yet ported a media player to the open-source image.
>...- May have other differences inside as well, but nobody seems to have done a comparison yet
Pretty much what you said is all that's 100% consistant, so far at least. MOST 8MB players have a TSOP ROM (easy to remove and replace with a new EEPROM), however I have a blue 8MB that has an epoxy glob instead. All 2MB so far have had chip globs for RAM. MOST all units have an epoxy glob for a processor, however at least one reported has a standard chip package. ROM checksums are all over the place, even of units of the same color, RAM size, and versions, /sometimes/ have different checksums, so there may be small differences in ROMs, even beyond the noted versions in the config utilities.