It even has "Multi-Disc Resume" feature. How does that work? How the heck does it know where I left off on a disk I took out, replaced another disk, but the first back in, etc? It must have to "write" a "tag" or something to the disk, but I thought commercial DVD's couldn't be written to!

I'd imagine the disc has something like a volume label or other unique identifying alpha-numeric data. The player just reads that into a memory slot, and stores the bookmark with it. Next time the disc is inserted, it looks up the bookmark associated with whatever ID it uses for that disc. If there is none, it would start at the beginning. No need or ability to write to the disc, if it already has a unique identifier.

Richard