(0.7 * / 100) * 3000 = $21 / month * 12 = $252 / yr
For that price, I'm better off just paying $60 / yr for CrashPlan, which is unlimited storage. I'd say that applies to anyone who has a terabyte or more of stuff to back up.
I've found that you can alleviate some of the headache by assigning the disks unique drive names. The reason for the deletion is that you might plug in your external HDD that gets mounted as drive F. You let it finish backing up, then disconnect it. If you later plug in a tiny flash drive that also gets mounted as F:, CrashPlan will see the contents of that drive and assume that you deleted everything from the previous drive and accordingly mark is as deleted in the backup.
If you mount the external HDD as drive Z:, however, when you disconnect it, CrashPlan will simply show the device as "Missing", but won't delete it unless something else gets mounted as Z while CrashPlan is running.
I should probably "test" doing a recovery from CrashPlan at some point, but I fear that even getting a third of it (1TB) would probably trip some sort of overcharge from my ISP.
Plus the price isn't too bad.
Echoing another comment, I'm not sure if this is a big a danger as a programmer's or operator's potential to wipe out all your data no matter how many datacenters it's located in, but....
I have data on my laptop, an external disk that I keep at home, and BackBlaze. The likelihood of all three failing in the same week so that I can't restore from any single copy is low.
I work at Backblaze, so I'm biased. :-) But the use case is important, meaning I wouldn't group together all "cloud storage solution" as one use case.
Backblaze does not have compute at all (like EC2) so Backblaze is a terrible choice for a company that will spend a lot of cycles analyzing the data stored in the cloud or doing compute on the data stored in the cloud. That is a much larger issue than the one data center for that use case.
On the other hand, it is my profound belief that for long term durability of data you should have AT LEAST three copies of the data stored by profoundly different vendors. Hopefully different file systems and stored by software written by different programmers so the same bug that affects one copy won't affect the other copies. Hopefully stored at separate physical locations. Put a different way: the only way to get more reliable than data stored at Amazon Glacier is to have one copy in Amazon Glacier, another copy on Google Coldline, and another copy in Backblaze. In that use case, the single data center of Backblaze is obviously a non-issue.