I re-created the test by shrinking the browser window on the Y axis and then pressing the button with the page mostly scrolled down.
Other than that, looks really cool! I particularly like the background blur. We're starting to see some really cool effects with CSS3.
There are some really weird bottlenecks in writing websites that are still beyond me.
(Linux Mint 13, Xinerama, Chrome)
It's a software problem, not a hardware problem. Probably just your browser.
Our frontend guy had a lot of issues with animation performance on the different browsers recently, he could probably speak to how big of a pain in the ass it is.
This is the first time I've seen Chrome performing worse than Safari on Windows (they're usually on par, with Chrome a little better sometimes).
More info in case it's useful to OP: Windows Vista, latest service pack I presume. 2.53 Core 2 Duo, a 4 year old graphics card (quite good for its day, but naturally not so hot these days), 4 or 5 gigs of RAM.
(checked on iPad, iPhone , MacBook air, iMac)
The iPhone or MBA, on the other hand, have far fewer pixels to push around.
Also, it seemed totally smooth on my mid-2010 iMac running 10.8.1 with Safari 6.
Is it really too complicated to simply link to a repo somewhere?