Me too! I'm in Mexico, with my Lumia setted for United States region. I noticed that, besides giving the answer in Celsius, it also displays a bit more info (mainly, text descriptions of the weather forecasts instead of only icons).
I also just noticed it today in New Zealand. Great to be able to ask for the weather without adding "in Celsius" everytime. Strangely, when I press the Cortana tile, it still shows temperature in Fahrenheit in the news feed.