Cloud computing interoperability

I was sat in the break area of a company a couple of weeks ago, minding my own business while waiting for a meeting, when I overheard a water-cooler style discussion at another table about cloud computing.

The main topic of the discussion was the expectation for many companies and individuals that while many are using cloud computing systems, like Amazon's EC2, but that longer term people want to be able to mix and match their cloud computing environments.

On the face of it, this seems like a fairly ordinary and reasonable request. Just because there are lots of different cloud computing solutions available, doesn't meant that you will always find the one that suits all of your needs. Looking across a typical organization and it's needs there are bound to be a wide variety of different cloud computing needs - web scalability, CPU time, storage - and it will all need to be supported somewhere. Different cloud computing services are not a problem, until you want them to talk to each other. Interoperability between cloud computing systems is the issue, but is it really a problem?

Deployment of the same application to different cloud computing environments is more of a nirvana solution than a practical one, for the simple reason that I want to be able to take advantage of whatever benefits a particular cloud provides; developing to the lowest common denominator is not going to allow me to do that.

But interoperability is about communication outside of the cloud, and surely we can leave that to SaaS techniques, rather than relying on some cloud-level support? That isn't going to work in all situations, of course. For some systems transference of data outside of the cloud increases costs, and may significantly impact the advantage of using a cloud in the first place, but I hardly think that interoperability should hardly be a barrier to using cloud computing if you have a need.