Facing strong concerns about control and security, the cloud-computing trend has drifted somewhat-- away from the notion that all computing resources can be had from outside, and toward a vision of a data center magically transformed for easy connections to internal and external IT resources.

Sales of cloud-related technology are growing at 26 percent per year--six times the rate of IT spending overall, though they made up only about 5 percent of total IT revenue this year, according to IDC's Cloud Services Overview report. Defining what constitutes cloud-related spending is difficult, the report acknowledges, though it estimates global spending of $17.5 billion on cloud technologies in 2009 will grow to $44.2 billion by 2013.

Hybrid or internal clouds will be the rule, however; even in 2013, only about 10 percent of that spending will go specifically to public clouds, IDC predicts.