Security in the cloud really is an issue, consider e.g. http://cseweb.ucsd.edu/~...

Security in the cloud really is an issue, consider e.g. http://cseweb.ucsd.edu/~hovav/dist/cloudsec.pdf - cross-VM attacks are real, and extremely scary.

(It is possible to get around this; e.g. Tarsnap doesn't trust the server much, and thus gets around the fact that it uses EC2. But that takes careful design and is probably impossible for many applications.)