Some months ago, I bought a external firewire DVD burner to use with my Mac. Today, I was browsing for something in System Profiler, and I discover this:
_NEC DVD_RW ND-3520A: Firmware Revision: 1.04 Interconnect: FireWire Burn Support: Yes (Vendor Supported) Profile Path: VendorSupport.drprofile Cache: 2048 KB Reads DVD: Yes CD-Write: -R, -RW DVD-Write: -R, -RW, +R, +RW, +R *DL* Burn Underrun Protection CD: Yes Burn Underrun Protection DVD: Yes Write Strategies: CD-TAO, CD-SAO, CD-Raw, DVD-DAO Media: No
Notice the DL under DVD-Write. Apparently this drive supports double-layer writing, and according to the NEC product page and a review at CDRLabs.com, it really does support it.
I did not know that. I don't remember buying this drive as a DL drive. Cool! I can now backup my Audible files to DVD.