Also, from some usability studies we've done at my job, it seems that most people are almost completely unable to deal with window management. We rolled out functionality for a while that broke the back button (poorly-implemented infinite scroll) and found that our pages performed very poorly, because people would lose their place and just leave. We kind of had assumed that most people would use tabs, but that turned out not to be the case at all.
Anecdotally, watching my mom use the computer recently was enlightening. She's been using computers longer than I have, and is very savvy with certain things (e.g., she still knows how to use Excel to solve problems better than I do, and I know Excel pretty damn well.) She seems to use browser tabs sort of like "processes", rather than "threads". For example, she'll have her "hotel search" tab, her "rental car" tab, and her "flight search" tab, and within those tabs, she'll stick to that topic, using the back buttons to look at different pages. When I switched spots with her, and started spawning a whole bunch of tabs from each tab, she started to lose track of things.
* Edit: actually, I almost never use the buttons themselves, but I use the functionality as I described. I use mouse buttons, gestures or shortcut keys, rather than the buttons.