I've used the loo now and then because of my grandparents. However, I often find it not a very polite way of saying where you are going or I get blank stares of confustion - where I am from. **most popular in my circles.
-washroom**
-restroom
-bathroom**
-ladies/mens room
-powder room - just to be different mind you
-I'm going to use the facilities...LOL
-many ppl say "I'm going to the toilet!". I don't like that way at all in public, but I'll say it around the hubbie. It's way different at home....