I wouldn't count on the 'steadily decreasing' part, s3 hasn't come anywhere near to following the downward price trend in hard drive cost per gigabyte/power per gigabyte, but even at todays costs, that's only $3900, which sounds pretty reasonable compared to what others are suggesting, if I did my math right, to keep 50 gigs around for 50 years. Of course, while I'd rather depend on s3 being around in 50 years than a raid in my closet, I still don't know that I'd give it great odds.

I don't think 'use rackspace /and/ use amazon' is a good strategy either, just 'cause if market conditions change enough that one goes under it's likely the other will to... and it's also likely that they could be bought by the same entity. you'd want to put one copy on s3, and then use some completely different storage method, like microfiche or or archival CD roms or something in a safety deposit box.