You might want to take a look at the podcasts, videos, articles and conference proceedings from the most recent WebWise conference (http://www.imls.gov/news/events/webwise07.shtm). Presentations from that conference made it clear to me that the solutions don’t lie in single answers like, migration,TDR’s,, etc. Rather, the experts at WebWise advise a holistic approach (their phrase, not mine) that incorporates these tools (and others) within broader practices such as data curation, archiving, media preservation, etc. Lots to think about, with some fascinating examples. I particularly recommend Priscilla Caplan’s workshop presentation.