Threat models and risks vary. SAAS offers aggregated data and appealing targets, though they may be well hardened. Much as I criticise Google, I find their claims of protecting data reasonably credible (not enough to be comfortable with it).
A distributed system with many known and unknown vulnerabilities and a readily determined network signature (nmap or similar) remains a bulk source. A determined adversary could scan all possible network space quite quickly and access data. With known targets -- monitoring your network traffic, knowing URLs or MXs -- they could target you directly.
NB: I haven't audited OwnClowd, nor am I particularly qualified to do so.