Jane/Fiona, a number of people, in various forum posts over the years, have suggested that we be able to add books without ISBN numbers. I've thought a lot about this because I too would like that ability. I don't know the structure of the EYB datebase, but imagine that allowing this could cause you problems.
To keep EYB out of having to track down every non-ISBN book (an impossibility), perhaps people could add their own books to the existing "book" database. However, I suspect allowing this would cause database quality problems. If/when that happened, EYB could end up handling way too many error notices, creating an administrative nightmare. Since acurate information is key to EYB's appeal, I don't like this idea.
Another approach might be to add another main category called "personal libraries", to the existing categories: "books", "magazines" and "blogs". The name of the new category doesn't matter. The new category could come with notice that EYB isn't responsible for the accuracy of, and errors in, this category. In other words, keep books added this way (unsupervised entries and unsupervised errors) separate and apart from the existing database.
I'm sure there are many other approaches, and am not sure my idea would work. I'm throwing this to the community for discussion. Any thoughts?