Steve Jobs announced Leopard will be available in spring 2007 and then handed out developer pre-release OS 10.5 to the developers attending the WWDC.
One thing I've noticed are is the tabs are coming!*
* Sorry if someone else noticed this ages ago :-|
From some of the videos released on You Tube you can see that tabs are being integrated in to more apps (okay, maybe just Finder) in a consistent manner:
Check out the cool effect of dragging a tab from out of the tab bar.