Well, I am fairly certain that Amazon S3 will handle multi-terabyte backups, mostly because their pricing tiers are for 1 TB, 50TB, 500 TB, 1 Petabyte, 4 Petabytes, and 10 Petabytes - and they make more money the more you store. Performance (at least in Singapore) is also pretty awesome if you have a gigabit connection.

I'll be interested in hearing of any experiences (particularly around performance) of someone attempting to backup on the order of 10 TBytes on the Amazon Cloud Drive. My guess is that if more than very few people do this, then either (A) Amazon puts an end to "unlimited" (and yes, I appreciated the scare quotes), or, (B) They rate limit uploads after a certain size to the point at which it just frustrates people.

For some of us, dealing with a vendor who finds greater usage on your part to be a desirable behavior, such that they actually give you price breaks the more you use, creates a business relationship that is worth more than the several hundred dollars/year you'll end up saving. (Of course, this is coming from the guy who has a $36/year AWS bill, $24 of which is S3 storage)

(Side note - When talking about Storage, it's very rare to use GiB/TiB - Data rates and Storage are almost always GB or TB).