The bug manifests itself in the form of an email from December the 31st, 1969 popping up in their email in-box. The message has no subject, sender or any content. This also seems to be limited to MobileMe and GMail accounts only.
There is a fix. But it involves 34 steps, apparently. Deleting the email has no effect.
I have several devices on various versions of iOS 4.x, and I only use GMail and MobileMe mail accounts on a daily basis. But I have not seen this bug yet. I feel a little left out as I was 2 months old in December 1969!
Apple have not commented on the bug yet.
Has this issue with iOS 4 hit you? Please let us know in the comments…