I was a VERY late convert to tabs, and I only use them for browsers now (and not all the time, either). I always felt that the OS X command-tilde functionality, for switching between windows the same way you switch through applications using command-tab, was superior. You're always switching between the most recently used windows, chronologically. You can even remember when something was several keystrokes back, and if you don't remember, you can see it in realtime.

It's insanely frustrating to try to switch between two arbitrary tabs in a browser, you have to use the mouse, and keep track of which tab you want to use. I was just running into this problem earlier today, switching between a doc I was reading and a tab I was working in.

Of course, having separate windows for everything leads to more visual clutter, and hurts discoverability a little bit.