I think "movie" is the most common term among us regular Joes in the U.S. and Canada, but in the movie business it's a little unsettled; if you listen to movie people talk, sometimes they say "movie," sometimes "film," sometimes "picture," and sometimes just "project" (as in "I'm really excited about my latest project"). And as you'll immediately notice if you hear or read an interview from the '30s, '40s or '50s, back then almost everybody in the movie business called them "pictures."
In England, it seems to be more common to say "film," and English movie people usually refer to everything as a "film." Other languages, like French and German, don't seem to have any nicknames that are as popular as "movie," so the word "film" is the all-purpose term for motion pictures. Of course, as more and more motion pictures are shot with technologies other than film, the term will start to seem anachronistic.
In North America, it's semi-common in some circles to use "movie" to refer to popular entertainment, and "film" to refer to art-house cinema. John Simon, the movie critic for people who hated cinema, liked this distinction so much that he called one of his books Movies into Film: his goal, he explained was to advocate the development of cinema from an entertainment medium (movies) into an artistic medium (film). This usage is also referred to in the musical Nine, based on Fellini's 8 1/2, wherein a critic sings:
The trouble with Contini, he's the king of mediocrities,
A second-rate director who believes that he is Socrates,
He never makes a movie or a picture or a flick,
He makes a film.
Get it? A film!
I also recall a Globe and Mail article a few years back -- I can't remember who wrote it -- where the writer explained that "movies" were run-of-the-mill entertainment and "films" were anything new or unique or different.
I dislike that movies/film distinction so much that I actually make a point of reversing it. If there's a movie I consider particularly annoying in its pretentions, I always call it a movie, never a film: Persona is just a movie, Ingmar, no matter how hard you try to pretend you're above all that.