The Apple site says this:
"Optical drive bay with SuperDrive (DVD-R/CD-RW) installed; writes DVD-R discs at up to 8x speed, reads DVDs at up to 10x speed, writes CD-R discs at up to 24x speed, writes CD-RW discs at up to 10x speed, reads CDs at up to 32x speed"
It doesn't mention DVD-RW, yet others on this forum mention using them, and even DVD+R and DVD+RW disks. I'm not bothered about +RW but being able to use -RW would be useful.
I just hope my G5 arrives on Monday so I can update my sig...