The final day of WhereCamp was an iBeacon hack day. But, i'm not here to talk about that now, but instead talk about Artefact cards
The cards are business card sized and blank. It seems like a con, but it turns out that they are really useful for planning out concepts and explaining ideas.
We were working on an idea for a capture-the-flag-style game using iBeacons and I was able to demonstrate by drawing pictures on the cards. I could have used Post-Its, but somehow the slightly more solid feel of the cards make them more readily accepted.
As an aside, 'card UI' is now a major design metaphor being used for mobile and web design. Cards are used to contain information for a single object and it makes it easier to build a responsive design (one that will resize itself intelligently for different screen sizes).