I had seen this
It's a funny thing, how fashion works. One weirdo in expensive clothes gets the idea to put his models' sweaters on backwards and that's "on-trend" for spring. The fashion bloggers & sartorially-minded see the runway shows and start wearing their sweaters on backwards a little early, setting the trend for the rest of us. The people like me--who peruse fashion sites and love clothes, but don't frequent NYFW--see it on models and bloggers and wear it out in real life, to their office jobs as receptionists. By the time spring 2012 is here, backwards cardigans are mainstream, normal, and so hot right now.
For me, the backwards cardigan is an easy way to remix a top, to stretch my modest wardrobe a little further, without having to go clothes shopping again. And god do I love a good low back on anything.