Firstly, K3b will happily burn and copy all kinds of single or multisession CDs and DVDs, and blank the rewriteable ones. It'll also encode your MP3 and OGG files into high-quality WAV format automatically, and burn them on to an audio CD. It'll do the same with your video files and produce a great video DVD.
Not only that, but K3b is as good at grabbing stuff off existing optical media as it is at putting data on it. As such, it will rip audio CDs and even multichapter video DVDs with consummate ease. The strength of K3b lies in the fact that it doesn't try to do everything on its own – it's folded the best tools for every task into its UI via plug-ins.
You can run it under Gnome, but it'll need a lot of dependencies. For simple CD/DVD burning tasks, Gnome users should probably go with one of the native Gnome apps instead. In terms of documentation, K3b bundles a four-year-old handbook and the low-traffic forum has more questions than answers. But these are superficial scratches on a rock-solid app that demands your attention.