Works in Canada for me. At home, it locates me as across the street and one house down. The only other time I've tried is was on St. Clair near Oakwood, and it nailed my position spot on. The only problem is since you don't have cell tower access or an actual GPS unit, ALL it can use to locate you is nearby WiFi points. So if people haven't mapped those WiFi points with an actual GPS unit, it won't work. Also, since you don't have constant internet access through cell towers, you have to be connected to a WiFi point in order for it to locate you.
Oh, and make sure you have the iPhone Google Maps application installed. Otherwise it never actually maps you out unless you hit Directions while it's trying to do so, in which case it opens up Safari at the Google Maps site.