The problem with cloud storage so far is that it can easily cost 10X the price of local storage.
IOW, I can build a ZFS cluster on Nexenta for say $25K (without support, but if you're considering this you should really consider the support unless you're a hard-core OpenSolaris guru) for 44TB of redundant, replicated storage.
That's a one-time cost of ~$0.60 per GB, and it can be amortized over a 3 year lease.
Just try and find pricing for Rackspace's uNAS service. ;-) We were quoted $2 per GB. Over three times the price. Wait, nevermind, that's MONTHLY and doesn't include transfer. So that's... $3.2M!
$3.2M vs $25K.
But make it fair and add the support. Also, go with a packaged Nexenta solution from Areasys. Hire a full-time SAN administrator. You're still looking at less than $500K to lease it vs $3.2M to host it.
Course, cloud storage is evolving very quickly, so this can and will change. Will it be cheaper? Possibly. Especially for smaller organizations without the time, skill or budget to purchase and manage their own in the short-term. Are we there yet?