Holy broken. This thing pops up "Mountain View" for me, presumably using geolocation, then refuses to allow it as a real city name. Also, if I fill in the "big" version and hit enter, the "little" version in the corner yells at me and tells me to enter both cities.
Long story short? I couldn't get it to give me a result no matter what I entered, and this was in two different browsers. It's broken.
That's a nasty error. Mountain View is stored internally as "Mountain View, California" and therefore the usual form of Mountain View does not match. Moreover, this error also shows that at least in this case partial matches are not recognized properly, as they should.
Needless to say, both issues are now on my list, and I'll fix them as soon as I can (I'm now on my "day job", expatistan.com is a side project).
In the meantime, as a workaround you can still use the site if you start typing 'Mountain View' and wait the two seconds that it takes the autocomplete to suggest the city. Then click on the suggestion and you should be set. Alternatively, you can just use this url the first time, and then change the second city on the boxes at the top right:
Long story short? I couldn't get it to give me a result no matter what I entered, and this was in two different browsers. It's broken.