I posted some pictures of my collection(on my personal site) of used Field Notes back in June; when the number was 32. And I realised yesterday when I finished another one that I now have used 50 of them. So I decided to do the same thing this time as well.
The way I use them have changed over the 2,5 years I have been a Field Notes user; from writing down ideas and notes to my the most important element in my GTD system. Some of them look like new and others are falling apart.
There have been times where I have used a notebook for six months, and there are times where it only lasted two days. But the usual life time is more like 7-10 days.
I'm going to make page, with pictures of all my used Field Notes early next year.