Media quality
Either for CDs, DVDs or DV-tapes, I never buy cheap brands, although it's true some higher-priced, well-known brands can sometimes be pretty bad.
I usually use Sony Premium-whatever, or TDK's, but I never re-write on them, which limits the damage anyway. It's for home use, so the budget involved is not that bad
For all digital content, quality of the content is fixed by the format, but the lifetime is fixed by the physical part of the media. CD's and DVD's are supposed to last around 20 years, which is due to the type of plastic used, and the process to "burn" them home, producing local heating peaks. The transparent layer will turn less transparent, etc... Regarding the DV tapes, it's the same problem, although not for heat but for demagnetization, so the storage place is important.
Which is why the "magical coatings" can help sometimes.
My problem nowadays is how long I can hope to keep data stored safely ? 1 year, 5 years, 10 years, 20 years ?