Wide bounds though. Migration services won't be inexpensive. No executive is going to sign off on the risk of doing such a migration without re-testing the whole thing. The effort is enormous: think Y2K. All we changed there was the date format. What people on the wild frontiers of Web 2.0 forget is the reality of enterprise computing. Changing the code is the easy bit. Long ago IBM had an excellent diagram that went something like the picture here. The techie bit of making the changes to the code is a tiny part of the overall effort (and that diagram doesn't include the increased ongoing effort of management).
Most service owners are reluctant to have IT rip the guts out of an enterprise application and re-architect its foundations; for the Cloud or anything else. The cost is prohibitive and the business outcome is zero change. When IT people pull their heads out of their technology butts long enough to look around and get a service perspective, they see that as far as the paying customer is concerned, large sums are being spent on an existing IT issues, which deliver no new service.
Some will see a way around this objection through Cloud services that do not require code changes: services that operate at the operating system, network or storage level to redirect requests out into the Cloud for fulfilment. This does indeed simplify the problem somewhat, but not enough. The amount of planning, negotiation and testing required for risk mitigation is still a large obstacle―just to solve problems which business owners expect to be invisible to them: cost cutting, scalability and performance.
Likewise solving the interoperability problem is not the answer here. The Cloud Computing Interoperability Forum (CCIF) has some major sponsors and just might make some progress here. Likewise the International Standards Organisation is looking at it. Neither of those initiatives will help the migration issue: whatever we change whether it is code or underlying platform infrastructure, it is a change. Real enterprise applications require a great amount of effort to change. This is inescapable. We need to cut costs and increase scalability in our existing applications for sure. Spending many millions to float our existing business systems on a Cloud isn't the right answer.
Very few organisations see such wild variations in load that they need resort to the Cloud for on-demand capacity. And the supposedly lower costs of management from service providers is a myth that the outsourcing industry still manages to perpetrate. When all the hidden costs―including lost IP, risk, migration, delays (ironically) and provider overheads―are factored in, the benefits are less compelling.