Lot's of new (true) html5 features, like: offline storage and web workers... And fast
" It has innovative new features that improve the way you view the web. And powerful new tools to help developers enhance and customize the browsing experience altogether. Learn more"
(Apple - Safari - Browse the web in smarter, more powerful ways.)
Don't ride the (true) buzzword wave too much ;) Web Workers aren't part of HTML5.