In the case of Nasuni and the Filer product; we have thought about this. All data is encrypted using your encryption keys, before being stored in the cloud. You're perfectly right to be concerned though.
Storing your data in the cloud, in the clear does open you to risk, which is one of the reasons cloud storage has not "taken off" for businesses in general, and why we do so much work to encrypt and protect all data before it is sent over the wire.
Oh! Another question (and I'm not trying to be a dick; I'm just really curious - data storage/retrieval in the cloud solves 1,000 other problems): how's Nasuni different than Cleversafe? Cleversafe runs their own data centers, I believe, but other than that, it seems similar: http://www.cleversafe.com/
Storing your data in the cloud, in the clear does open you to risk, which is one of the reasons cloud storage has not "taken off" for businesses in general, and why we do so much work to encrypt and protect all data before it is sent over the wire.
We wrote a blog post on this recently, in fact:
http://www.nasuni.com/news/nasuni-blog/security-and-the-nasu...