Thought I'd throw my 2 cents in for this popup. It's nice and simple to use, it does what it does, popups up a simple screen with you sales pitch, and it's free, I recently paid $20 for a similar one that I could only use on one site.
Someone mentioned you can't link out, not true, you can put links on any text you are using in the Tiny MCE editor and you can make them open in a new tab/window or in the parent window, easy really.
My only gripe, which is why I'm giving it 4 stars is that you can't put a background image in the popup, at least I haven't found a way anyway.
One bug I found... I added a image to the tiny MCE editor to use as my sales pitch popup, no text just a complete image with all the sales text I wanted so that I could have a background, it worked, but later on I wanted to change the text so resorted to typing text in the editor and formatted it, and made do with the white background. see ozecigarette It wasn't until I opened my website on another screen that I noticed that two popups were coming up, the old one and then after it the new one. WP Super Popup only handles one popup so this was weird. I fixed it only by going to the database and finding and deleting the record in the wp_popup table.
That needs looking at, other than that, great popup