Pros:
- Cloud is distributed; therefore, in theory, robust and redundant.
- Cloud can be inexpensive as archived storage.
Cons:
- Public clouds (e.g., Amazon) are not secure; few financial institutions (banks, brokers) allow their DBAs to place sensitive information on the cloud, even if encrypted.
- Public clouds can be expensive for archival storage, moreso than a redundant leased data center.
- Network bandwidth to public clouds is poor, whereas leased lines can be run to non-cloud datacenters with relative ease.
- In practice, for large storage, public clouds are often not distributed or redundant: the data resides on a particular set of disks, somewhere.
My personal preference for large backup is a redundant datacenter (or leased storage) at a reasonable distance from the primary data center. As a Wall Streeter on 9/11, I can assure you that 50 meters is not a reasonable distance, and that while one might be able to crash a plane atop a datacenter, the ensuing fire and water damage can make the structural issues moot.