I have been keeping sketchbooks since 1995, and for a while I was at the pace of one to two books a year. Then I had children, and sleep deprivation and a full-up schedule of being a caregiver slowed me waaaay down.
When I first started keeping sketchbooks, my high school art teacher told me that the books should be more than a place to record your ideas. He called sketchbooks "a reflection of you"--over time my sketchbooks have been both intensely personal and a place to record that bit of inspiration before it evaporates into the ether. I always kept one book at a time, but now I am starting to branch out. The explosion of art journaling has definitely increased the variety of pre-made books available which is great. I love being able to get my hands on a book with heavier weight paper. I like to have a sturdy substrate to build on.
The most interesting thing to me, as an artist, is how many ideas go into the sketchbook and just stay there. If I never had another idea, I would have enough fodder to work for the rest of my life in my sketchbook collection. There are plenty of concepts that seem really promising at first, but wind up being too meh* to ever get to the point of becoming a stand-alone work. It's the ideas that follow you around all day, tapping you on the shoulder begging you to consider how to resolve their issues that even get to the point of serious consideration. I suspect this is much the same for anyone who creates--the world is full of ideas, inspiration is everywhere! But you only have 24 hours in a day. The work that you choose to shackle yourself to and carry out to the end of it's creation has to be worthy of those precious hours.
Which isn't to say that I haven't ever painted over a canvas, because I have. I have been moving around with the same 3 large canvases that I used for a final project in 1999--and every few years they get a facelift. If you have a piece from me I promise that I won't come to your house and paint over it. Unless you want me to--in which case, let me grab my paint and I'll be right over.
I've included a slide show of random pages out of the various books I have worked on for the past two decades.
*meh--bland, boring, mundane.