it looks like a software / firmware problem to me , a thought echoed on apple's discussion boards
cd-r's and dvd+r's won't show up on desktop and in apple profiler and hard disk utility they show up as readable only..
BUT
itunes will burn on the cd-rs and idvd will burn on the dvd+r's , as long as you access the discs through the programs
and most oddly of all , they show up on the desktop once they're burned..
strange , eh ?
i recently ran that smc firmware update from appple and before it everything was wrking properly !