Via my dad, comes this link to a PC World article asking "Do Burned CDs Have a Short Life Span?". The expert in the article suggests that for long term storage, use magentic tape to store files you want preserved for decades. For your average home user, burning copies to CD's I think is still feasible as well as copying the files to multiple machines/hard drives to hedge your bet.
Opinions vary on how to preserve data on digital storage media, such as optical CDs and DVDs. Kurt Gerecke, a physicist and storage expert at IBM Deutschland, has his own view: If you want to avoid having to burn new CDs every few years, use magnetic tapes to store all your pictures, videos and songs for a lifetime.