We’ve seen a couple of friend’s Yahoo! mail accounts get hacked recently. When one of them got hacked again I did a little bit of research and I was surprised at how prevalent this is. If you have an SBC Global or Flickr account you should also be concerned as both of these also link to Yahoo! mail.
Here’s one of the many articles I found: Yahoo Email Hacked! What I Learned. What You Can Do.
Edit: I’ve been told that the information in the article about location is out of date. If my information is correct Yahoo! no longer provides location data which is a shame.