I'm talking about actual surround, which most things seem to be in these days anyway (not that that's always the best option, necessarily).
But honestly, they just turn it on and watch it whatever it's set to, and I can't believe they can't tell the difference between different settings. As in, they literally don't seem to notice that there's a difference between stereo spread everywhere, and surround, where there are significantly different things going on in different speakers. Plus, some of the settings on the amp (like virtual) just sound awful.
Personally, I find it weird having dialogue coming out of all speakers, especially when it's coming from behind. I also have a keen ear, and having that slight change in quality when spreading a track across all speakers when it's designed for two grates on me. So my preference is to keep it in traditional stereo.
I think the only time I use multichannel is when I'm watching YouTube, or sometimes when I'm streaming music (depending on what it is). I typically opt for playing a CD on direct mode where possible though.
I imagine how well the sound is spread will vary though depending on your reciever. The quality of speakers would also likely play a part in how noticeable minor changes are.