Let’s say that you have a situation that you want to have a modal window show up only once for each user. It’s actually not that difficult although lots of Googling around got me nowhere. I am choosing to use FancyBox for my modal window, but feel free to use your modal framework of choice. So let’s get down to business.
My application uses Facebook Connect and grabs the users Facebook Proxy email address (FB app developers will know what this is). So I check if that’s the email I have for the user. If yes, then I pop up a modal window on page load only once to get their regular email address and possibly a password so they can login to their account without Facebook Connect if they want. When the modal window is shown, a variable is set in the cookie (note that this cookie is shared with authlogic for sessions) to ensure that the modal window isn’t shown again.