This was the first time I encountered this in real life. I had seen some of this in the Photodiarist blog before. There are Yarn Bombers in Leipzig too and I will show you some pics of Leipzig soon. I found those yarn bombings in Leipzig only after I had seen those in Austria.
Anyway, more on this topic here: http://en.wikipedia.org/wiki/Yarn_bombing
I think this yarn bombing is a fabulous idea.
Are there some yarn bombers where you live? If so want to share some pictures? Post them on your blog, comment here and I'll link to your post.