Some people use tabs for keep related pages into one window, while another set of related pages (but not related to the ones in the first set) sits in another window. There is probably some other UI concept that covers this case, although only time will tell if it works better than tabs.
I, on the other hand, mostly use tabs as a task list. If there are N links on a page that need processing (i.e. search results), I will quicly go over them with a ctrl-click, and get N tabs. Then I will start prcessing each, pressing ctrl-W when I'm done. This way I do not have to click back and forward, and I do not have to remember were I were if I decide to pause.
I can't see anything replacing tabs for the latter, short of some convoluted craziness that will only exist to "have something different". Anyone want to prove me wrong?