To be specific, you'll see this offer the next time you login to the game. If you've yet to try CastleVille, you'll be given a link to do so, and after just a few play sessions (making it through the tutorial and a bit further), you'll have reached Level 5. Once that's done, just head back into your city and you should see a window containing the image at right, celebrating your achievement, and placing your 20 free Zoning Permits into your inventory.
Sure, that might not be enough to actually help you expand your land in CityVille, depending on how often you do so, or how many citizens you currently have living in your town, but it sure beats asking friends (over and over again) to send the permits the old fashioned way, wouldn't you say? I'd expect more games to jump on the cross-promotional CastleVille wagon in the very near future, and we'll make sure to let you know what prizes launch through those promotions when they do.
In the meantime, let us know - will you play CastleVille to receive your 20 free Zoning Permits in CityVille? Sound off in the comments.