Bill Prentice, you said,

>>The [British] Library as a whole is working on a mass storage setup, 
>>and as soon as we have access to that, we'll ingest like crazy and ditch 
>>(or at least stop relying on) recordable optical media ASAP. 

In this scenario, what will you rely on for backup?  Do I recall reading that you will have mirrored servers at separate geographic locations?  Not being able to afford that, we are moving toward enterprise server based storage for .wav files with backups on the discs in question located elsewhere.  In addition, there will be backups on SDLT.  That provides two magnetic storage options (HDDs and SDLT) and one optical.

>>I reckon a good quality, appropriately burned silver backup is safer in
>>the *medium term* than a gold backup on batch-identical media.  

Well put.

Thank you all for the thorough treatment of this subject!