Nice work - bookmarked. Minor things:

* support for alternate names (e.g. The Hague vs. Den Haag)

* some way of knowing when a city wasn't found - right now if I type the name of an unrecognised place then it isn't clear that the time displayed is no longer valid

* optional vertical layout for phones, and (to go with that) offline support? Perhaps not quite so minor, I'll admit ;)

Oh, and re. the "programmer-friendly" comment in your article - I'm one and I don't find those sites at all friendly...