Very, very cool idea; the city and state of any address can be discerned by a zip code, that’s a given. Yet every single web form in existence always asks for city, state, and zip. It’s needless work.
Ziptastic! provides a public API endpoint for anyone to send a zip code and receive a JSON encoded object back containing the appropriate city and state. Neat idea. The demo is easy enough to grok. Check it out.
The only problem I see is that as it stands right now, this really only works on zip codes like the name suggests; that is, this only works for American zips, there is no way to look up international postal codes.
(via Daring Fireball)