If you listen to music over your iPod or computer, it's safe to say you're listening in stereo.
Cars are a different story; they can have speakers in all sorts of places, so I'll grant that music in the car may not be in stereo.
But the music itself at least started out as stereo; MP3s and CDs are strictly stereo, so unless you listen to a lot of 5.1 channel, stereo is where it's at.
Most, but not all post-1980 films are available in 5.1. So if you have a 5.1-channel home theater, surround is where it's at. But there's a catch; most people, I'm guessing at least 75 percent, listen to movies with the speakers built into their TVs. Which are, after all, stereo speakers.
So again, stereo wins the popularity contest. And if you're watching movies on a portable device or computer, yup, you're listening to stereo.
The movie companies are certainly aware that once their film leaves theaters most folks will be listening to the stereo mix. They make sure it sounds great.
My personal home theater is a 2.0 (no subwoofer) system. I'm no fan of special-effects-driven films; I go for dramas and concert films. What can I say? Stereo fits my lifestyle/aesthetic perfectly.
I'm not claiming 5.1-, 6.1-, or 7.1-multichannel sound is "bad"; not at all. In fact, I think the quality of movie surround mixes has steadily improved over the years. I listen to them when I'm reviewing gear all the time, but I don't need to hear surround at home. For me film is about the quality of the story, acting, and cinematography. The sound? Sure, it's extremely important, but it's there to support the picture.
How about you? Do you listen to movies in stereo?