How do you compare Cloud Hosting Providers??

[Niklas]

Hello!
Given the new buzz word "cloud" is thrown around a lot, there needs to be some sort of resource that can educate and be referred to by users seeking cloud hosting.

How should you compare cloud hosting providers?
What makes one cloud host better than another?
Is it important to know whom they use for their cloud 'backbone'?
How secure is your data?
Is the cloud only a small group of computers or an actual commercial cloud?

Can anyone please share some tips, plus information on how to evaluate and best determine which cloud host is best to their needs? e.g. The right questions to ask and how to evaluate a provider's service?