I could be wrong, but outside of parts of New Jersey, I dont think it's very popular at all.
I'm sure you can probably get it somewhere, but I cant ever recall anyone I've known eating it in other places I've lived in the country. Food Network did a bit on it a year or so ago and mentioned it as being a "Jersey Thing".
any part of the country that had immigrants during the depression has their own unique "meats" of questionable origins. Scrapple comes to mind as one of the more well known items.
Cincy has something called goetta. It actually tastes pretty good if you don't ask how it's made.

http://en.wikipedia.org/wiki/Goetta