These guys have been more than three years constructing their architecture which consists of… your spare bandwith and disk space. By means of brand new technology based on mathematical polinomial analysis, your files are stored all over the social storing network minimising the redundancy (yes, there’s no whole file stored in a single computer neither a single computer storing a whole file, always taking into account the probability of a computer being offline). So that, hail to private cloud computing.
And I find funny (but clever) their business model: "Need more storage? No problem. Get the storage plan that fits your needs. Our technology allows us to offer extra storage at extremely competitive rates." (extracted from Wuala’s web, the underlined is ours). Sure it is!, but don’t miss their R&D costs during all this three years plus the extraordinary profit they deserve due to the clever breakthrough.