I never use bookmarks.
Well, in the sense of using the kind of bookmarks sold at bookstores. Instead I tend to use whatever is handy: A receipt, a piece of paper from earplug packaging.
I wonder how many seriously addicted book lovers/readers like myself actually use "real" (i.e. commercially produced) bookmarks. My guess is that "real" bookmarks are used by people who want to look good rather than those who actually devour books at rates of several a month.