Would you write in a notebook if it came with a warning that there is no guarantee that the ink will stay on the page or the pages won’t spontaneously combust? Or that there is no way to know if other people are reading your notes? That you don’t actually own the information you write down?
Yet that is how most cloud service providers work.
There’s no guarantee that your data is safe, secure, or even yours anymore. Sure, it would be bad for business if they lost all your data, or you suddenly saw that blog post you had on Google Docs posted somewhere else, but that might be an acceptable loss to a giant company. The point is, the data is no longer in your control.
I’m not saying all cloud service are bad. I use many of them myself (as does most of the world). But it’s important to know the risk with what you are doing. Don’t use any service as the end all solution.