You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
I think all the brown-eyed people shall remain in the island until a visitor says "I see at least one person with brown eyes". 'Cause as you said not everyone knows that everyone knows that everyone knows... there's someone with brown eyes.
I think it should work if everyone knows there are only two possible eye colors... when all the blue-eyed people leave in one night, that's equivalent to someone saying "I see 100 people with not-blue eyes" and there are only 99 other people on the island. But I'm not certain. ;)
