I think mat board is the greatest thing ever invented (well, maybe after the internet. ha!)
It's great stuff that cuts easily with a razor blade so anyone can make things. I've made small furniture out of it as it's sturdy and cheap. I was lucky to get a whole box of small pieces at a yard sale a while back.
I just made a pile of books with mat board inserts. Made it easy to fill them since you don't have to cut paper or card inside. Just paint the edges and voila! Done. I want to make some antique-looking books next. After all, all houses - even dollhouses - need lots of books!!!
* And what are you working on on this "lucky" day?