The March, 2005 issue of Popular Science has a list on page 74:

"Archival Life.  These are estimated life spans of standard storage media.  To be safe, transfer your data to new media every few years.

CD/DVD+/-R    2-15 years
CD/DVD+/-RW    25-30 years
Hard drives        3-6 years
Flash drives        10 years"

Without accepting this as gospel but allowing it to provide a sense of proprtion, the choice among the options they mention seems clear- and that is bypassing issues concerning how the CD-RW is made and what it is made of.   

I think it fair to state that the consensus here is that external, single unit storage on an inactive hard drive is poor archival strategy.

Experience has shown that, when faced with limited funds, adminstrators usually choose to save new data rather than transfer old data.  Preservation through migration requires an inexpensive medium using a minimum of inexpert labor. 

A number of simultaneous alternate possibilities have been raised. Many on this list are more knowledgeable than I about these other devices and encloding methods.  I, for one, would be quite interested in explainations of what they are, with a minumum of jargon and with definititions of any acronyms.  I would welcome a sense of the costs of each, advantages and disadvantages, and informed guesses as to the direction of future cost by those with experience using these options.  An essential facet is data concerning standards relating to each to avoid future decoding nightmares.

Steve Smolian