All these "amazing" examples of what CSS3 can do are... well, amazing, considerings the limitations of CSS2. But also dangerous, considering "flash based web sites".
Remember that a user may want to see the same page several times. Copy-paste parts of it. Have a closer look at a specific item on the page. Cares for the content, not the weird movements it is doing.
If you look at very CSS-heavy website around + JavaScript it brings to its knees my poor old computer (it's ridiculous, it's only 2 years old), it feels bulky and laggy, prevent me from copying sometimes even looking at things...
Doing complicated things with heavy CSS animation is (relatively) easy, but bringing to end users a simple yet elegant and useful design should be a webdesigner's job, not these hacky-scrolling features, stuff that swirl around making it impossible to copy or even to look at. For your nice CSS tricks leave it as easter eggs for your most attentive visitors, they'll love the feeling of having discovered something hidden.
In CSS animations, less should be more.
The downsides with flash were the accessibility issues and the fact that it was a browser plugin. This is baked directly into the browser and if coded correctly I think can be used sparingly for a good effect. As much as we browse the web for content, as long as it is displayed effectively (in a static or dynamic) manner is what counts.
I think now's the time to start working on a browser plugin that disables these "beautiful animations".
- Email introduced, email overused (spam, grey spam, newsletters) we started using spam filters.
- Ads introduced, ads became overused, we install ad blockers.
- Flash introduced, flash became overused, we installed flash blockers.
- Facebook/twitter/sharing Widgets introduced, became overused, we install widget blockers.
- 2012-2014. CSS animations and transitions introduced... you get the picture.