Alessandro,
There's a few reasons this could be happening. Additionally, another user just posted that they just subscribed and aren't seeing posts. When we test, it's working for us, but it's possible (though unlikely) there's been a change on Facebook's part that's causing issues for some users.
I just registered on the site and got the message below. I'm not seeing any updates on login, if I should be:
Sono tornato su Aloysius Dance!!
Things to check:
* If you have "Automatically Log Facebook Users In", try disabling that and logging in. We were notified of a bug last week that can cause login posts not to occur with this setting. It's with a few other settings enabled as well, but this is a good test to see if it's affecting you.
* Change the login message so that it's different than the registration message. Facebook can prevent duplicate messages from being posted, so if the 'new' message is the same as the last message on the user's wall, it may not show up for that reason.
* Make sure you've approved the application, and given permissions rights (likely the case since my registration worked)
Hope that helps get you started, but definitely let us know if you continue to see issues.