Are you using cloud computing? Chances are even if you don't know what it means you've been actively using the technology, which recently has been defined by companies that provide online storage and Web 2.0 applications.

That's the result of a new study on cloud computing released by the Pew Internet & American Life Project, which found that 69% of U.S. online users have been using cloud computing in one form or another.

The Pew study of 2,251 adults cited use of e-mail services like Hotmail, Gmail, and Yahoo Mail by 56% of study respondents as a popular use of what has come to be called cloud computing. Of course, Hotmail, one of the first online e-mail services, was in widespread use well before the term "cloud computing" became part of the computer vernacular.

The study by Pew associate director John Horrigan was unveiled -- appropriately, perhaps -- in the offices of Google, which is heavily invested in cloud computing.

In addition to the e-mail programs cited above, another example of cloud computing that has long been in use is online photo storage. Pew said 34% of respondents said they have stored photos online, while 29% said they have used online applications like Google Docs or Adobe Photoshop Express.

The study found that users overwhelmingly like the convenience of cloud computing and that the phenomenon has particularly caught on among younger audiences. Pew noted that cloud computing applications were generally favored by nearly 77% of people between the ages of 18 and 29 in its survey sample but by just 27% of respondents over 65.

In spite of the generally positive outlook for cloud computing, it has a gloomy side over privacy concerns. When asked how they would react to their stored data being sold to another party, 90% responded negatively.

"Sixty-eight percent of users of at least one of the six cloud applications say they would be very concerned if companies who provided these services analyzed their information and then displayed ads to them based on their actions," the Pew survey stated.

Many companies in the tech industry use the words "cloud computing" in describing their own products and services, although aspects of the term could also be applied to time sharing, software as a service, and even on-demand computing. To help understand how companies large and small use cloud computing, InformationWeek has published an independent report on the subject. Download the report here (registration required).