Glacier looks great, until you look at the retrieval costs!

If you use it as a backup strategy and you're going to need access to all of your data then you're going to have to extract it from glacier in a relatively short time period. This might cost you an arm and a leg (relative to the storage costs)!

See: http://brandt.github.com/amazon-glacier-calc/ for an online calculator.

If your use case matches the price structure in that most of your data is write and forget and occasionally you'll need a small piece of it back then it's a fantastic service & as last-ditch backup options go it's a whole lot better than nothing at all!

(edit: not sure that calculator is entirely useful since it appears to squeeze the entire download into a single 4 hour period.)