Hi Richard:
I'd worry even more about the dual-layer DVD media, just based on historical experience with multi-layer plastic products.
I would bet that for every one DAT mechanism ever manufactured (and I'd guess maybe 50% of all ever made, or more, are no longer in good working order), there have been 20+ laser-bearing drives made that can read most or all formats of 5" plastic discs. And for every DAT tape ever spooled, maybe 50+ blank CDR's have rolled out of Asian factories. That's a good harbinger for the long-term viability of the CDR format.
This is an example where industry standardization on a method and form factor is a very Good Thing. I'm hoping very much that DVD+/-R is a continuation of the Good Thing but it's pretty early to pass judgement.