> some USB device (phone, Mp3-player, camera)
> Linux may auto-mount it. Does the subsequent un-plug without dismount create any significant risk of data-corruption, ot just annoyingly logged errors?
Data corruption happens only when some cached data was not completely (i.e., partially or not at all) written to the device. As long as the user (or his desktop environment) did not actually try to write anything, everything should be fine.
Furthermore, all these devices use FAT(32), and that FS is so simple that a partially written file usually does not affect the data structures of other files.