The basic functionality of being able to add any zip code and being able to display it is not given.
England and the Netherlands have non-numerical zip codes, such as "W11 2BQ". See http://en.wikipedia.org/wiki/Postal_codes#Precision
The field will not let you enter such a zip code.

Typing any zip code longer than 4 digits will also add a thousand delimiter automatically, which is also displayed on the output. Cannot be used like that for the zip codes.

Suggestion: convert field (and sample data) from Long to String.

(Small workaround for the output in contacts.ftl:

<span class="postal-code">${contact.zipCode?string("0")}</span>

- but ultimately the field fix is necessary for the non numerical zip codes)