AFAIK, PowerBook superdrives are "-" only.
Newer desktop drives (Pioneer DVR-106 or higher, and certain Sony models) work with either "-" or "+" media as long as you have OS X 10.3.x.
However, OS X's "+" media burning support is limited to data only; no "+" support in the iApps. Finder burning is supported.
I've had no problem using "+" media, both +R and +RW, on my G5's superdrive.