The cloud is meant for file exchange and access anywhere, but it can serve as an additional backup option. It's not a perfect backup solution though, there's always a risk of it going out of business/catching fire/getting raided by the NSA/hacked. Consider leaving a spare copy of your data on a drive at a friend or relative's place.
The Wuala model isn't very economic as it's free, and encrypted, meaning reduced options for "intelligent advertisement" and so on as a revenue streams.