I'd like to address some of your concerns from this thread. If you were seeing errors that said something like "Your WordPress.com account, username is not authorized to view the stats of this blog.” or “You are not a member of this site.” that problem is being caused by a permissions error. The stats are still working, but your account needs to be sorted out. If you contact support, we can fix it manually for each of your sites, but we are also working to find a better global fix for this problem.
The "invalid_signature: The timestamp is too old." error is a different problem where your web server's clock is not set correctly. See http://wordpress.org/support/topic/jetpack-problem-invalid_signature-the-timestamp-is-too-old#post-2010749
Please start a new thread for any other troubles.
We want you to be happy. WordPress.com experiences very little down time overall and I understand when you temporarily lose access to your stats, it's frustrating! I see that you guys really love your stats. :-)
Next, I'm working through all the replies in this ticket. I will make sure if you listed a URL that it gets checked. I will try contacting you via your account if I have questions. And if you see this thread and still need help, please send the error message you are seeing directly to http://en.support.wordpress.com/contact/ and we will take care of it!