The great video on the special effects of Bringing Up Baby was deleted along with the user's account, but fortunately he uploaded it again at a different account. Which is an excuse for me to bring up a question I've been wanting to pose for a while: what are some types of special effects that tend to hold up well over time, and others that don't?
The essence of a good special effect is that it's not recognizable as a special effect. Some effects are always going to be noticed because they portray things that can't happen in real life, like teleporting or boat travel. But most special effects are used to fake stuff that, theoretically, could be done for real. Like in Bringing Up Baby: it would be possible for people to be in the same shot as a leopard, and in fact Hawks originally intended to do a lot more shots that way, but in the end, special effects were used to make it look like Cary Grant was standing next to a leopard. And in Citizen Kane, special effects are used in virtually every scene to fake sets that Welles didn't have the money to build, or crowds of extras that Welles didn't have the money to pay.
It's fun to have these things pointed out to us after the fact, but these effects are successful because most people aren't aware of them. When I saw Bringing Up Baby for the first time, I knew Grant and Hepburn were in front of a rear-projection screen in the car, but I didn't realize that Baby was part of the screen rather than the car. (Presumably because Baby was filmed in the car, in front of the rear-projection screen, and then combined into one plate; I'm assuming they didn't actually take him into a car and do the road filming with him in the car.) I didn't notice that Kane was making his big political speech in front of a fake crowd. And so on. Most of these effects hold up over time; audiences don't watch the movies and point out how fake the effects look. At least not when they watch the movies for the first time.
But do some special effects have a special ability to hold up over time? Probably not, at least not exactly; it depends on how they're used and what they're used for. Rear projection can be fairly convincing for some things, though it's almost always totally unconvincing when it's used to make it look like the characters are somewhere other than in the studio (a car, a park -- though it works fairly well for trains). I think that CGI has a way of dating really fast, to the point that characters look like horribly fake cartoons almost as soon as the movie comes out, but of course there are plenty of uses of CGI that are more convincing than that damn CGI rodent at the beginning of Indiana Jones IV.
I do have a feeling, and it's only a feeling, that models often date very badly. There are good model shots, obviously, but a lot of the special effects that date the worst are models, like the awful model village at the beginning of The Lady Vanishes or the model train in The Smiling Lieutenant, which got the only unintentional laugh in the screenings I've seen over the years. Models are kind of like CGI (they're both three-dimensional constructions, after all); if they're not perfectly executed, they look like silly toys.
On the other hand, I think matte paintings have a habit of holding up well. Again, there are lots of bad matte shots, but when I'm surprised to find out that a shot in an old movie was faked, it's usually done with a matte. There's something about the way mattes blend in with their 2-D filmed surroundings, or maybe it's just that the painter has more of a chance to match his work to the style/look of the film than the model designer does. Whatever the cause, I (as a young viewer) was more easily fooled by the likes of Peter Ellenshaw than I was by almost anyone else.
Finally, I think the worst special effects shot in a great movie may be that stupid fake bird at the beginning of The Seventh Seal. It doesn't hurt the movie, though. If anything it helps by announcing that this is not a big lavish historical epic, but a low-budget, small-scale movie that happens to have a historical setting.
Which leads me to the final point: of course, the key to making any special effect work is for the movie to be good to begin with. We're much more likely to notice fakery when we're not caught up in the story.