Well first of all the optinpop website is like the worst website I've visited for years. If you're showing as much adds for your stuff, noone is going to pay you.
Second the plugin has virtually no otions at all, so be prepared to loose many readers if you really use it.
Should offer support for only showing on custom pages, or only showing when clicking on a link (and then for that damn specific link having a specific page to show in a lightbox).
Other plugins are way better, well and actually work too. OptinPop did not work on my site, but how it worked and the minimal options was enough for me to write this topic here.
Pretty angry about the cr*p they did, otherwise I wouldn't even bother (ain't the first plugin that does not work for me, but the most annoying since I started with WordPress 3 years ago).