Should I back up data stored in the cloud?

The reference link is below, but I can tell you the answer in a word: YES.

We need to learn from the Microsoft "Danger" Debacle (or the T-Mobile Sidekick Debacle, if you will), and the Amazon Kindle disaster.  Don't expect companies or people to give a damn about you when they mess up.  Sometimes, it isn't even the companies, it is some ignorant fool behind the scenes with a score to settle with the company.  Sometimes it is a disaster (whether Cyber or real).

Even worse, don't even ask the question when the data in Google Docs is pretty easy to back up.  Take a look at http://1st-soft.net/gdd/ and see TWO ways to backup you docs on Google Docs.  They're both pretty simple... Okay, I guess the Python one isn't that simple for most people, but the GreaseMonkey/DownThemAll one is!  With tools so simple to use to backup that data, why would you not periodically do that?

Reference: Should I back up data stored in the cloud? | Adventures in IT - InfoWorld.