Ever thought why do you need a 'cloud' for storage and not manage the data on the internal servers? It is a combination result of people not being able to manage their data (like someone filling up the garage with crap and parking the car outside, even during a snow fall!).
The storage data growth is 10-times every 5 years and an example halo effect is explained here: one employee sending a 1.1MB email to 4 colleagues takes up 51.5MB total storage.
Source: IDC, "The Diverse and Exploding Digital Universe," March 2008