A friend of mine in the cloud world, James Urquhart, who now blogs at CNET recently posted about cloud maturity models. It's worth a read.
I've added a comment, which I'll also leave here (a tidied up version and a mental reminder for myself to check that what I'm pressing is a preview and not a submit button.)
=== comment ===
Good post James,
I especially like "achieving an open marketplace is essentially cloud computing nirvana, and the ideal to which most enterprises should logically strive to achieve" but of course, I'll add onto this.
Such a nirvana will only be achievable (without the loss of strategic control and pricing competition to a technology vendor) if the standards which the marketplace is built upon are operational open sourced pieces of code rather than specifications (it's an old post from July'07 but it covers the basics).
Such open sourced standards (the equivalent of open design patterns, such as the open SDK for GAE) will allow competition and service innovation through implementation. The standards themselves will help encourage portability, the open marketplace you describe and hence consumer innovation through componentisation.
As for "I believe this open market is inevitable, as the economics are just too powerful" - well it's either going to be open or we will see government intervention in the field to force the market to behave in such a way.
You can create the illusion of open marketplaces with a proprietary stack but it is no more than an illusion.
Anyway, good post.
As far as maturity models go, well you've seen this before and though it's old and tongue in cheek, it does have some serious point to it.