Ah yes, guarantees.
Guarantee: [in english] A formal promise or assurance that an obligation will be fulfilled or that something is of a specified quality.
Guarantee: [in computing] A marketing term used to indicate an aspired to or theoretical level of service that a provider hopes, one day, to achieve. (See also: "up to", "unlimited", service level agreement, "bug-free", maximum talk time.)
The nice thing about [IT] guarantees is that they are almost never testable before committing to them, have many, many exceptions, get-outs and preconditions, hardly ever come with any penalties for their breach and can frequently be modified, nullified or have additional conditions attached at the whim of the supplier - even if you can understand the language used to define them and have agreed that understanding before signing on the electronic dotted line.
Cloud computing is no different from any other major infrastructure change. You can believe all that the salespeople tell you and dive in headfirst, or you can take a more considered approach and take the time to build a relationship of trust with your new best friend. Whichever approach you decide (or have it decided for you) to take, always have a Plan B, frequently ask yourself: How can we disentangle from this operation? and always, always keep your CV handy.