mrFlashcard stores a some information about decks and cards you make and import, including:
This website also uses some analytic tools to track usage of the website:
Currently the only personal information that can be provided is an optional cell phone number to SMS a link to your deck to your phone. The plan is to save this number so later on you can choose to receive SMS messages as reminders to study more cards. Of course, if this feature becomes available, it would be opt in; the site won't text you without your permission.
Currently, unless you shared your decks or cards manually with others, the site doesn't share them with anyone.
To delete all your information, either delete each card one at a time, or contact email@example.com. Or, feel free to just leave your cards alone.