At least with an 'old school' serial engraved into the unit, you stand a better chance of having someone discover that it's stolen, either by the actual number, or by the fact that the punk selling it has scratched it all up trying to eliminate the number!

I disagree. I think the current method of having it in Flash is the best way. Engraved serial numbers can be easily sanded off or re-engraved by any thief (and they do precisely this sort of thing all the time so it's old hat to them), but there's no way for them to change/erase the serial number in flash without also making the player ubootable.