When using a full-screen app in Lion, you can move the mouse to the bottom of the screen, then move it down again to show the Dock.
Double-click in Safari’s tab bar to create a new tab on the right.
Note that in the upcoming OS X 10.8 Mountain Lion, this feature may be removed (though the OS is in private developer beta until its scheduled launch sometime this summer). In its version of Safari (5.2, to be exact), the tab bar in Safari for the Mac mimics the iPad’s in that tabs stretch to take up the full width of the bar.
via commenters at one of my other sites, Wind on a Leaf