1) Trello is used by some as a digital Kanban board. A bit thing is Kanban is the idea of a "blocker" - on physical boards this is usually a big, in-your-face, bright red sticky note. The point is that it jumps out at you and gets the team to swarm in and address the issue. Trello didn't really have this before (yes, you could use labels but it wasn't obvious). Now you can slap a big WARNING sticker on the thing and people will notice.
2) Trello has been trying to move away from being strictly a tool for software developers. Look at the marketing home page - the example board is for an Art Project, not a software app. With people using Trello to plan weddings [1] or to help their kids with homework [2], they are aiming for a different market than techies. Ever have a chore list when you were a kid? And what did mom put on it when you did your chores and earned a reward? Yup, a sticker. Brilliant move if you ask me.
[1]: http://www.22ideastreet.com/blog/2013/09/12/the-tech-behind-...
[2]: http://heartofwisdom.com/blog/get-organized-with-trello-list...