We do not look at your data without your permission. We do look at certain "metadata" in order to know who added how much data, from what source, and when. Some data can also end up in our error logs, e.g. a malformatted timestamp. Finally, we use Google Analytics to collect site usage information, including response times, network locations and browser versions. This data is not linked to your account.
Your data is sent over secure connections, but is not stored encrypted.
Note that you are not required to provide us with any personally identifiable information, other than a working email address (when you create a permanent account), and a valid credit card number (if you are signed up for a paid plan).