Sure they do. A whole bunch of changes that have been accumulating in the WebKit nightly builds just became available when Safari 4.0 was released, not the le

Sure they do. A whole bunch of changes that have been accumulating in the WebKit nightly builds just became available when Safari 4.0 was released, not the least of which was Squirrelfish Extreme, which was branded as "Nitro" in Safari 4.x. I'm not sure how one could miss that, between Google, Wikipedia, Apple marketing pages and webkit.org.