Say, I have a mere 2TiB of historical data (various junk I made or collected over last ten years or so). Storing on them with Amazon is $20/mo, and if I want to look on that photos from 2008 I have to wait for several hours just to find that I misremembered where they were stored and pulled out wrong files. And unless it happened that I uploaded a good amount of data on that exact day, I'll have to pay for downloads.
Other offers for unlimited storage are Cyphertite at $10/mo, Crashplan at $6/mo, Carbonite at $100/yr, AltDrive at $4.5/mo and so on. While they're probably not-so-unlimited (they don't say that, but I guess one won't have much luck storing a petabyte), less respectable than Amazon, and most services lack an API and require to use not-so-trusty proprietary software that has to be sandboxed properly, Glacier doesn't look like a good deal to me unless we're talking about backing up some either quite big data (like tens of terabytes) or relatively small amounts of data (less than 500GiB).
Disclaimer: I have no affiliation to any of companies mentioned above. Just happens that I'm currently fleeing from Bitcasa (they suck hard) and looking at various options to not maintain a self-hosted NAS.