World metros ~ Aug 30, 2006
wrote an interesting tool which I refound thanks to ion, where you can select logos for all subway systems you've ridden.
World metros I have taken:
Got at b3co.com!
So, Helsinki (Finland), Madrid (Spain), Porto Alegre (Brazil), Mexico City (Mexico), Caracas (Venezuela), Guadalajara (Mexico) and Valencia (Spain).
I guess people living in countries where it's easier to travel between each other, may have caught more metros 
