I've had canonical tags on my todo list for a while. Yesterday I got around to implementing them. I applied them on my top three templates. I was trying to be very careful not to make any mistakes. I tested all the combinations I could think of.
Naturally, I messed something up. I forgot about the various languages the site is in. I canonicalized all the other languages to the English site. Oops. It was like that for about 24 hours. I hope googlebot didn't notice too much and that traffic to the international sites doesn't take a hit.