Go to your Profile then select Modify Profile. To enable email select that option in the "Notify by email.." drop down.
You can also check "Show a popup.."
(http://dl.dropbox.com/u/6759805/Profile.jpg)
Thanks!
Hmm. Mine was already set to 'Always'. I've set it again, so we'll see what happens. Maybe not for a week or two though.