What about the integrity of the company behind it? That's another concern, and just recently a decent sized company specializing in online storage was forced to close their doors after suffering a massive data loss. Upwards of 45% of the data the company was hosting for as many as 20,000 paying customers was lost, apparently permanently. Why the company had no backups is anyone's guess, though I'm sure anyone paying for it assumed that “The Linkup” was on top of making sure their data was safe.
What's worse is that apparently storage problems for the company started over a year ago. It brings into question just exactly how safe your data is, and proves that you can never go wrong with having local backups. It also provokes issues of trust. How long will it be until you (say, from a business perspective) put data online and not have to worry about it one day disappearing?