Last week, a maintenance upgrade of musescore.org was performed to Drupal 6.14. This introduced two bugs: subscription emails are not sent anymore and the post preview doesn't work anymore either.
A patch for the subscription email has been rolled out and that seems to have fixed it. However, you may have received a flood of emails which were waiting in the queue. Sorry about that. This will happen only this one time.
Looking into the preview issue right now.