Apple's logo artists have infused the iCloud logo with some mathematical elegance. In this case, the golden ratio or φ.
The circles in the 'puffs' of the iCloud are sized in a ratio of 1:1.6, an approximation of golden ratio, as discovered by Australian designer Alan van Roemburg. It seems unlikely the proportion was unintentional; Apple's artists simply have an acute sense of the history of design and mathematics.
The golden ratio has been around since at least Euclid and Pythagoras. Fans of the Da Vinci Code should know it too, as Dan Brown has referenced φ several times in his books. No wonder iCloud seems so elegant and aesthetically pleasing.
Hat tip to John Gruber
Update: The original source of the image appears to have been Takamasa Matsumoto.