I had the same issue since upgrading to 3.5, I tried all other suggestions: remove and reinstall plugin, activate and deactivate + reconnect to wp.org. If you have FireBug (for firefox) installed and try to view the status, you’ll see heaps and heaps of errors in the console related to JavaScript files hosted on wp.com (for the admin section).
I installed the plugin mentioned above “Use Google Libraries” and it works now.
Some people mention changing themes also (to the default 2012 one), but that didn’t didn’t work for me.
I have WP-SuperCache installed, so I turned it off and back on just to be sure. Just for the record it was still logging stats(I could see them on wp.org even when I couldn’t view them from the JetPack dashboard.
