What happens is, well, nothing happens. You put in a DVD or a game, a disc symbol appears under "video" on the menu. You put in a Blu-ray, nothing.
Funnily enough, the disc that didn't work that brought this to my attention was Scott Pilgrim. Then I tried Kick-Ass, which had worked before on the PS3. Nothing.
A couple nights before, I watched a library copy of Angel Heart (DVD) with a barcode on the disc. It whirred loudly in the PS3 for a moment, then played fine. I'm wondering if the barcode fucked up the inner calibration in some way.