Perhaps I'm just bad at doing things, but I noticed this way before the internet. Something like this random-walk path: reading a semi-scholarly book, run into an endnote, turn to the end of the book to read it, find a concept I don't know, open up my dead-tree World Book encyclopedia to find it, follow up some cross-references there, eventually remember to go back to the book, try to remember what endnote I was reading and where I got there from, restart. The internet makes it easier, but the pattern doesn't seem new!

It's even worse in university libraries, where you can actually follow up all the references by grabbing them off the shelf. The number of books piled up around you with post-it notes marking pages is roughly like the number-of-tabs metric...