Your article piqued my interest. I've had the same thing happen to me over the past 2 weeks as well. My one board (http://pinterest.com/JenniferBakerCo/social-media-training/) has increased in followers by 20 (or so) per day for the last 14 days... But it's just that one particular board.
Thanks to you and the other user's suggestions and insight as to the "why"!