As InfoWorld's David Linthicum pointed out a few weeks ago, the public cloud isn't likely to save you money. What you really get is a tremendous amount of pay-as-you-go agility that you'd be hard-pressed to realize with on-premise resources. At its core, that's what the cloud really does well, and it truly deserves attention for it.
It's vitally important, though, to realize that simply because your services are based somewhere else on hardware you don't own doesn't mean you'll spend less time on administration duties. In fact, you may even create skill set gaps within your IT department where there previously weren't any -- forcing you to rely upon much more expensive external help.
I found a good example this week. A fairly large company I work with currently runs its email on Microsoft Exchange 2003 and is considering a long overdue upgrade to Exchange 2010 -- and determining whether to move to Exchange in the cloud is part of that decision.
On paper, it looks like an excellent idea. Hosted Exchange -- whether through Microsoft BPOS or a third party -- is a relatively cheap pay-as-you-go service . Even better, all day-to-day management (save user provisioning) disappears and is handled by someone else. Or so it would seem.