We interrupt our regularly scheduled programming today to bring you an announcement of a new participant entering our little sphere of gamebook hobbyists: Jake Care is a mathematician and a gamebook enthusiast. He's got a new blog set up over at http://jakecaregamebooks.blogspot.ca/, and he's kicked things off with a very exciting post about linearity in gamebooks.
I think, for myself at least, his terms for categorizing gamebooks by linearity, "Linear," "Convergent," "Divergent," and "Free Roaming," will likely enter my personal vocabulary pretty promptly. The only thing I would add to that discussion is that I think these are not mutually exclusive. A single gamebook can have aspects of each of these. For example, I (like Jake) really like Free Roaming, and I often try to include at least a section that's free roaming, even if the whole book can't be.
If you haven't checked out Jake's website yet, please do. Welcome to the club, man :)