I think this is nice, especially w/ customizable questions. But let me play devil's advocate and ask: what is PopFeedback going to do for me that KISSmetrics or another couldn't?
Honestly, right now it's just price (and even free surveys are customizable) and the fact that you can setup a follow up action such as asking for an email, asking to follow you on twitter, or like you on facebook. So if the user is already engaged enough to answer the question, he/she is more likely to give you their email or follow you on twitter/facebook. But we have a few other ideas on what to add to make this even more useful and differentiate ourselves better.
I also thought of rolling my own. Thanks for saving me time :)