It's definitely hard to trust a small fly-by-night unknown operation like DropBox.
Not to politicize this, but considering DropBox put Condi Rice on their board recently, there are definitely possible trust issues there. Besides, known or unknown doesn't really matter -- we've already seen it revealed in the Snowden docs that Microsoft was complicit with government demands for user data access. So, all I'm saying is, buyer/user beware.