The Undo option sounds good, though. Is that a feature of Opera? (I haven't seen it in FF)
Yes. Opera 8 also has a wastepaper-bin for closed windows, where the windows closed by the pop-up blocker also appears. (Though the "open only requested windows" do a good enough job that I don't think I've ever had to open a blocked window.)
But the biggest advantage with tabs is of course for people like me who don't want too many windows around. (Opera can of course work with multiple windows instead of tabs, if you prefer. Or both. You can drag a tab to the desktop, and it becomes a new window.)
Look at me - I'm starting to sound like an Opera salesperson.