"The cloud gives companies an easier way to manage all their technology," says Sinha, of Google Apps for Business. "It moves all the hard, boring parts into the sky and makes it invisible." Companies seem to like this. Sinha says Google Apps for Business sales have tripled over the past year. The company doesn't break out numbers, though, so it's hard to know how big an impact it is having on overall revenue growth.

Still, Google's cloud efforts are part of what makes it a buy right now, say analysts. Trading at about $490, down from above $640 earlier this year, Google looks cheap, says Michael Scanlon, a stock analyst at John Hancock Asset Management. Down here, the stock trades for less than 10 times expected earnings, if you take out its $36 billion in cash. Scanlon believes the contributions to growth from cloud computing and mobile search are being overlooked by investors. "Anything that can get people into their ecosystem benefits the wider franchise," he says.

Of course, by attempting to move business computing to the cloud -- and away from the PC -- Google and other cloud providers pose a direct threat to Microsoft, which makes a lot of its money by selling desktop operating systems and business software deployed inside companies.

But don't count Microsoft out, because it has cloud offerings of its own, known as Azure and Dynamics. "Its public cloud offerings polled the strongest of any vendor in our survey," says a recent report on the sector by Morgan Stanley. "Microsoft is likely to gain the most from a broader adoption of public cloud environment."

Besides, as useful and popular as the cloud is, it's not clear the PC is going away. "The cloud won't replace conventional computing, because it is still convenient to have your data and applications on one machine," says Michael Cusumano, a professor at Massachusetts Institute of Technology's Sloan School of Management and author of "Staying Power: Six Enduring Principles for Managing Strategy and Innovation in an Uncertain World." "And remote access doesn't always work well. It may be at least 10 years before we have such ubiquitous broadband wireless connectivity that people will want to give up their desktops or laptops. It may never happen."

Amazon, through offerings called the Elastic Compute Cloud and Simple Storage Solutions, is another major player that provides a combination of software services, and the platforms and infrastructure to run it all.

Getting pure

Unlike these giants, which are involved in a lot of different businesses, several smaller companies represent more-focused ways to invest in the cloud.

Salesforce.com serves as a nearly pure play. It offers software that helps corporate sales teams track leads and sales as well as share developments inside their companies, all from the cloud.

This is a stock that traders love to short, or bet against, mainly because of a rich price of 74 times earnings. But the company has defied such investors. "They own their market. They are taking share," says Rudow, at Thrivent.

On the infrastructure side, VMware plays a big role by selling software that helps cloud providers subdivide servers for private use by customers. "It's like two kids sharing a room, and not knowing it," says Scanlon.

And of course, EMC is a major cloud play because it sells storage devices and the virtualization and security software that make them run. "They have a lot of the key technology. When you are setting up cloud servers, it is hard not to buy something from EMC," says Abhi Gami, senior analyst for the Invesco Van Kampen American Franchise Fund (VAFAX), which has beaten the Standard & Poor's 500 Index ($INX) over the past year.

Among the "enablers," Accenture and IBM stand out as public companies that should continue to get meaningful business by helping companies set up in the cloud.

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Of course, among the big risks here are concerns about the safety and privacy of data in the cloud. Openshaw, at Deloitte, says such fears are overblown. "Security is good, and probably better than what most individual organizations can muster on their own."

Besides, having all your data up in the cloud and not on your laptop can be a blessing, says Google's Sinha. "Your data can't just get up and walk out the door with the device."

At the time of publication, Michael Brush did not own shares of any company or fund mentioned in this column. Brush is the editor of Brush Up on Stocks, an investment newsletter.

Michael Brush is the editor of Brush Up on Stocks, an investment newsletter. Click here to find Brush's most recent articles and blog posts.