I've never heard of the 'other' folder before. So I go look for it and find a message from an old college friend getting back in touch. From 10 months ago. Thanks FB.
Same here. We are supposed to be the tech savvy crowd, so I dare say that if that happens to us you can safely say there is a big usability problem there.
Just a little notification along the lines of "You have x unread messages in your 'other' folder", perhaps only once a week, would have gone a long way in solving this.