I too am a dedicated highlight-reader, precisely because it's so easy to lose my place when scrolling. I found myself reading somewhat slower (perhaps due to trying to understand what was going on and how it worked), but I wasn't clicking the mouse maniacally, either.
Hey guys, I'm designing an annotation product that uses highlighting as part of the control scheme, and I'm wondering if you'd be willing to test it at some point in the future and see if it interferes with your reading habits. You guys are hard to find! Also, any other 'highlight readers' if you reply here or PM me I would be very grateful.