> "Trello is about putting lists of cards on boards. That's it."
100% this, for me.
That's how I'm able to get people to use it. They ask a lot of questions about what means what and assume it's more complicated than it is. As soon as they realize that the top level metaphor is seriously just a board with cards, they're like "Oh! that's really cool. I can use this" and they're off.