Re: A writeable CD left on window sill
The life expectancy of an optical disc in my house is directly proportional to how well I hide it from my kids. One left on the window sill wouldn't survive long enough to be damaged by UV. Seriously. As an example I've got a couple Veggie Tales discs that are coated with what looks to be a mixture of peanut butter and super glue. (In case you're wondering, they're in my fix-it pile until the kids forget about them so that I can throw them away without drama).
On the other hand, I can count on an optical disc in a case (be it a jewel case or a paper sleeve) in my non-environmentally controlled - and, even worse, non-dust-proof - storage unit to work regardless of how long it's been in there. I've got discs from the 90s that have been in storage except when I need them for as long as I've had the unit they still work just fine. In fact thanks to the recent death of my home file server I'll be pulling quite a few of them in the near future.