I know this is an old study, but I'm amazing at how many people use the back button. I wonder if that's how a lot of people deal with search results that didn't pan out (they hit back to go to Google, instead of opening them in a bunch of tabs).
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.
As for forward and back, yeah I use them a lot too. Normally via extra mouse buttons or keyboard though.
I find it more amazing how many people use the forward button. I think I've probably used the forward button less than 10 times in the 18 years I've been using the web.
To the 60% of users who use it - when do you find it useful?
"wait, what was that page I was just on?"
"wait, did that page really say that?"