I was googling about various digestive-related things, and, since Google generally knows what I need and I don't always act like a grownup when no one is watching, I was phrasing my queries very childishly. For example, "How long does it take food to turn into poo?" (Answer: an average of 2 days)
I soon noticed that Google's autocomplete was always using phrases that contained the word "poop", not "poo". For example, if you type "My poo is" into Google, you'll get a drop down full of autocompletes saying "My poop is" every colour of the rainbow.
People who have done more research than me suggest that "poop" is USian, and "poo" is more British. A site:.ca google (which, I realize, is not the most precise research method ever) gives 298,000 hits for "poo" and 198,000 for "poop", so it seems that "poo" is more preferred in Canada.
However, even if you go to google.co.uk, the autocomplete still suggests "poop" when you type in "poo". "Poop" also turns up in the google.fr and google.pl autocompletes. (Google.de and google.es retain "poo".)
Which one do you use?