Tabbed browsing is used in (at least) Galeon, Mozilla and Opera (though Opera's idea is more like "emulation of Windows taskbar").
Personally, I use Mozilla and I have found tabbed browsing be essentially useless on large screens - on large screens, it's much more convenient to use separate browser windows.
Yet, when my monitor refused to cooperate and I was forced to use TV screen with tiny little 640x480 dimensions, tabbed browsing is extremely convenient - the browsing buttons and menus stay on one area of the screen, other pages can be switched to through the tab bar. It must be noted that in Mozilla, opening a new tab is faster than opening a new window.
Also, Mozilla's tabs avoid most of the pitfalls of Opera's MDI UI. There's no "main window" in which subwindows (which cannot be moved out of the main window) appear. Instead, there's a "main" browser window, always of preferred size, that has pages in tabs - and pop-up windows still appear as separate, independently movable pop-up windows. Opera 5, on the other hand, had a window in which the pages were always as sub-windows that could be independently managed - this was sometimes somewhat confusing, and the only practical thing to do was to keep all subwindows maximized, thus emulating the "tabbed" behavior of Mozilla. (I have heard Opera 6 doesn't mismanage the windows as badly as Opera 5...)