iCloud icon of Apple was already in use for more than 3 years

Apple's iCloud icon was already in use since the launch of MobileMe online service that was introduced firstly on WWDC-2008 keynote by Apple. It was introduced to form a basis of cloud icon for the users of iOS and Mac devices.

MobileMe was a service for users of Apple products. With this service users could sync email, data and other documents over the Cloud. iCloud icon has a similar impression as that of MobileMe icon. One of the most impressive and interesting features of iCloud is its mathematical involvement. It uses the principles of Golden Ratio as shown by the following example.

Scott Hanselman reviews that it was in circulation even before Apple introduced it as an icon of iCloud. He explains the origin of the icon and how he found it, 

Funny thing about the Golden Ratio, if you look for it, you’ll find it everywhere. It’s intuitive. Cool, also that they attribute this icon and it’s “brilliance” to the Apple Designers, except the icon isn’t from Apple, it’s straight from Pictos 1. I know, because we bought it from them for our site. Plus Pictos 1 has been around for years. It includes a regular cloud, clouds with arrows up and down and a lightening bolt cloud. 

Further Reading:
Hitechanalogy