I store a disk image as back-up, just incase. Only had one client have issues, they wanted a refund, but it turned out to be their player messing up, as the dvds worked fine on every other player/computer they were tested on (which they even admitted, yet still persisted for a refund).

I've not had any deteriate over time yet, and it's been 7 years since I started producing DVDs. Just don't use those pesky sticky labels!