You're right, in my personal testing it does appear to be about 2x faster.

The big perf wins:

* Fewer box shadows

* Fewer gradients

* Fewer semitransparent borders (a big performance problem, especially in chrome - I've seen > 10x performance slowdowns when using rgba borders & border-radius: 0 - see Chrome's tracker [1])

* Simpler rules (fewer styles to cascade)

1. https://code.google.com/p/chromium/issues/detail?id=170882

this should be the most upvoted comment