Indeed, this feature is called 'Tab View,' and can be invoked by the button mentioned, a trackpad gesture, or a keyboard shortcut!
New in Safari 6 is Tab View, which shows you all open tabs.
Use one of these methods to show all tabs.
- Click the "Show all tabs" button in the Tabbed browsing bar.
- Pinch in with two fingers when you are viewing the webpage in its full size.
- In Safari select View > Show All Tabs or press Shift-Command-\ (⇧⌘\).