Safari is getting a new JavaScript engine, thank god! Having suffered through some of the quirks of Safari, I am happy they are moving on. Maybe the new Squirrelfish engine will be more inline with Firefox or the dreaded Internet Explorer and eliminate some of the Safari specific workarounds (read: hacks) that have been added into so much of the front end code.
If we are all really, really lucky, maybe Safari/Webkit will get a new CSS engine too. Oh, happy days.