When many regions are used on the same same page, they are slowing the page down considerably.
Check http://sourcefabric.github.com/BookJS/test.html for a simple demo.
Check http://sourcefabric.github.com/BookJS/test2.html for a demo of lots of flows.
Check http://sourcefabric.github.com/BookJS/test3.html for a demo of long flows.
Could you please retest this with a newer Chromium? There's been some performance patches that landed in WebKit/Blink in this area.
This seems to have been resolved with recent improvements