I notice a lot of movie reviewers talk about how CG is overused in movies, and while that may be true, they also say it looks obvious whether CG or actual props are being used. Maybe it's because I don't have a 16ft by 9ft screen, but I honestly have never been able to tell the difference without someone telling me. Is it really that noticeable?

CGI* =D
And also I think it really depends on what the image is, if you take something like star-wars laser blasters than yeah it's pretty obvious, but certain characters in modern films could be actors in makeup or could be completely generated and sometimes I can't tell the difference

If you notice it then then you know that you have seen it.
If you don't notice it then you don't know that you have seen it.
If you don't know you have seen it, you think it wasn't there.
This distorts your perception of how good it it.

IMO, CGI is a crutch that is overused. Not because the effect itself is bad or played out... but because it makes it really easy to make visually appealing movies that are otherwise empty.

Acting, writing, story, etc all become less important when you have good CGI. And good CGI is everywhere now... which is partially why modern movies really, really suck. Nobody is interested in creating substance anymore. As long as there's flashy explosions and cool effects, suckers will keep buying movie tickets.

See: any Michael Bay movie and any comic book movie... which comprise 95% of movies that have come out in the past 7 years.

Horns is pretty good, they only really use CGI for one scene but it is lol epic.

^+1 Disch
This is why I watch anime, even though they're entirely CGI they're nice simple art style and focus highly on story (well the decent ones do)

I don't think people notice half the CG in movies. (Not all of it is spaceships and aliens.)

Here's an example:
http://youtu.be/2Qv0pD-Nfag?t=2m50s
The commentator points out the CG mask, but I can't even tell how he knows it's CG?

You can tell if you look close.

It's harder for some people to spot with the motion... so here's a still image from that video:

http://imgur.com/bwY9Xxc

It looked like it was copy/pasted onto his face. (Look near his brow if you can't spot it, it's more noticeable there)


EDIT: Though you can spot it with the motion too. If you keep an eye on the edges of the mask when he's moving his face around, the mask doesn't quite move the same as the rest of his face does.