I dog-ear pages, but not to keep track of pages. Generally I do it for my Lit class, if it's a good example of theme or something of that like. As for general reading, I'll just remember the pages, or throw a random piece of paper into it. I remember that I used to, with hard cover books, put an end of the dust jacket in, which worked well enough. I don't read hard cover books that often anymore though, so...