It's been a year since the last Enterprise 2.0 gathering and the verdict is in: Cloud computing is for real and it's here to stay. The problem is that no one can define what cloud computing is.

David Berlind, chief content editor of TechWeb, set the stage for an Enterprise 2.0 session on cloud computing by urging the audience not to worry about a definition of cloud computing, but to take advantage of its benefits as they appear in increasing force.

Cloud computing is rolling into many IT shops and the companies delivering it view it from different perspectives. At the session, it became clear that three leading suppliers of cloud computing -- EMC, Google, and IBM --- approach the cloud differently but are united in some common benefits as well as some curses of cloud computing.

To Mike Feinberg, senior VP of EMC's Cloud Infrastructure Group, cloud computing is a "disruptive" technology that encompasses many different aspects of computing. Feinberg noted that many IT users began getting comfortable with storing data off premises in the late 1990s, which has helped prepare them for cloud computing. Today EMC still offers a backup service in the cloud, as well as a series of other cloud offerings.

EMC is pursuing what it calls "cloud-optimized storage" through its multipetabyte EMC Atmos offering, which delivers massive scalability in a user-defined environment. It dictates how, when, and where information resides. "Many people have trouble finding where their data is," said Feinberg, referring to an eternal IT dilemma.

"The value is to do other things and to try new things," said Feinberg, indicating that a large cloud computing configuration can help users experiment without danger. "You can put your toe in the water."

IBM is in a somewhat unusual situation because in a sense it's retrofitting cloud computing to its $20 billion business that runs critical IT infrastructures throughout the world. "We think that the cloud is a new way to solve old problems," said Sean Poulley, IBM's VP online collaboration services.

Google is credited with naming the phenomenon, when chief executive Eric Schmidt talked about "cloud computing" at a conference in 2006. He said: "I don't think people have really understood how big this opportunity really is."

The irony today is that IT professionals still can't define cloud computing, but they're beginning to understand the opportunity involved in it.

Google, of course, has taken advantage of cloud computing through its pervasive Google Apps suite, which covers a brace of applications from Gmail and calendaring to Google Docs & Spreadsheets and Google Video.