At least that's the latest - don't hold me to it. So they said May 11th, right? Well, according to googleandblog, the rollouts officially started today - May 14th. That doesn't explain the few reports we've heard about some folks getting the update, but it would explain why they've been so rare.
My source (linked above) says 10% will receive Cupcake on the 14th, but then states that %5 will be complete by the 18th. Clearly, the numbers don't jive. But that doesn't mean there's nothing to this at all. Maybe 1% will be updated by the end of today.
EDIT: my source has corrected their post - 1/10th of a percent for the 14th. T-Mo News sorta confirms.
So, whether it's good or bad news, this is the reported schedule:
Be brave. Be patient. The best of luck to you. Oh, and please let us know when you get Cupcake by commenting on this post - it could be useful for other readers. It's just as likely to torment them... but still.