Dan Farber has an interesting piece on mainframes and IBM's cloud strategy.

"As proof of its mainframe devotion, IBM is in the process of internally replacing 3,900 servers with 33 mainframes by the end of 2009, he added, noting that issues such as data center space and energy savings make the mainframe a cost-effective investment. Since 2000, units of installed mainframe capacity from all vendors has grown from 4 million to almost 13 million today."

He quotes IBM software chief Steve Mills: "Our corporate buyers are running mission critical apps, and they are not going to pick up their businesses and take them to some amorphous and ill-defined data centers. The cloud as some amorphous concept that meets all needs and requirements is science fiction."

Seems to me that mainframes running in service bureaus are part of the cloud, which includes more than one model of computing.

Semi-related: My favorite big iron story from IBM: Project Kittyhawk, set up "to explore the construction and implications of a global-scale shared computer capable of hosting the entire Internet as an application."