Choppy for me with a Nvidia GTS 450 (proprietary drivers) on Fedora 23. Every part of the massively long pipeline from HTML to DVI has to be perfect to get smooth playback. It seems we are some way away from reaching that yet.
Smooth on my Intel (HD Graphics 5500 / Broadwell, 2015) graphics. Nvidia's GTS 450 is 5 years old, so I don't think "we are some ways away" is necessarily true, but it is of course still very wasteful.
It is 5 years old, but is able to render scenes far more complex than the on on this page natively.
Smooth for me on Intel HD4000, open source drivers, current Ubuntu.
Smooth for me on IntelHD3000, open source drivers, Linux Mint 17.2 :)