On Trello, I have my notifications set to instantly, but I'm not receiving email updates in my Gmail. Is there a bug or problem I am unaware of?
Perhaps the issue is that you are not subscribed to any cards. Trello does not send email notifications of all changes that are made to your board. Try subscribing to a card, and then ask someone else to comment on that card, and see if you get an email.
More information from their blog: http://blog.trello.com/introducing-subscribe-get-notifications-for-any-card/