Dog Ears or Bookmarks?

So, I had this loooong discussion with a friend this weekend about whether or not it is okay to dog ear the pages of a book. This then also led to a debate about jotting notes into the margins of a book. Oh boy, we sure didn't see eye to eye on these ones. As someone who used to be VERY neat with her books (Bent spines? Sacrilege!), I now think that dog earing and - come to think of it - writing into the margins is okay in some situations. I suppose textbooks and low-priced editions I use when I'm teaching/researching would fall into this category. For all others I use a bookmark. 

My friend, however, didn't agree at all with this division into "work" books and "pleasure" books. She only uses bookmarks. Full stop. No discussion. I, of course, respect her opinion but I'd be interested in what my (still few) readers think? Are you a dog-earer or a bookmark-lover? Do you possibly have any unusual/interesting bookmarks that are special to you. Please post your two cents in the comments section...