Afaik they removed the top tabs in a later beta, although you could still enable them by changing the preferences via the terminal. In the final release of Safari 4 however the top tabs were completely removed and you won't be able to get them back.
Anyways, you could hide the status bar (cmd + /) and bookmarks bar (cmd + shift + b), which gives you a lot more space. You can also use Google Chrome instead and use its full screen option. Chrome also uses Webkit, so it's very similar to Safari. There are also tons of similar extensions for both browsers, so you won't miss any functionality.