The most important question about Trello, to my way of thinking, isn't addressed on its website in any obvious place: where is the content of boards, lists, etc., stored? If on my computer: details?
If on Trello's website (the cloud), is it stored encrypted or in plaintext (details)?
What other measures, if any, are taken to ensure that Trello data is forever recoverable and secure?
I would never use Trello for any real-world purpose until these questions are answered.