To add my anecdotal 2 cents:
I've been burning CDs for over 10 years. I've been using them as my exclusive backup system for 6 years. I switched to DVDs for backups about 2 years ago.
My oldest burns, 10 years old, are audio CDs and for the most part they still play fine. However, those were on the original, expensive, and better quality $5-$7 each media. A few songs glitch for no real discernable reason (no scratches, no dirt), so I must assume that there is some deterioration. Being simply audio, it's not the end of the world.
As for data backups, I have burned around 500 optical discs. I had to do a major recovery last year and I found that almost all the CDs (and few DVDs), most on generic media, read ok. There was 2-3 or so CD-Rs that would not read on my newest LG DVD-RW drive, but read fine on a CD-RW drive. I could not discern any logical reason for this (not brand, type, color, etc, dependent). There was maybe one file that was completely unrecoverable out of the hundreds of discs, so my mileage was pretty good.
Keep in mind, my self-programmed backup system does immediate file-level verifies after write. With this I catch about 1 disc in a 50 that for whatever reason didn't burn 100% perfectly, and I simply reburn it. I attribute this to flaws in the media where the burn will succeed but a chunk of data will be unreadable. I would never trust the burn without an immediate verify.
Because of the strange reading issues described above, I immediately implemented a reburn-burns-3-years-old policy, which actually was quite easy to add to my program and requires no extra effort. It also staggers the reburns by file so that there isn't this sudden overwhelming mass of burning I must do.
I have since switched to Verbatim Data Life Plus "archival" "lifetime" grade media. The look & feel is discernably better quality than generic, and Verbatim has excellent web pages describing the advantages (mostly having to do with the better sealing of the dye layer and better plastic).
The media I use: http://www.verbatim.com/products/product_detail.cfm?product_id=3CE81E3E-674F... My price is $26 for a 50-spindle, delivered to meetings. Around 50c a DVD is not bad for protecting your data. The 15-25c premium over generic isn't much money in the big scheme of things.
They make a zillion different types, so check them out at verbatim.com. Most of them are available to me at good prices.
We'll see in another 10 years how well these held up!