Up to Chapter Seventeen, 69.8% of the way through the manuscript. Still liking it, which is good, but getting itchy to work on the second book already!
Which brings me to the subject of transitions. Truman Capote once said that, "Finishing a book is just like you took a child out in the yard and shot it." This kind of feeling can stop you from finishing, because you don't want it to end. Or you have to wait while your book is going through the slow process of agenting, publishing, etc., and you are essentially helpless to affect it, which is a bad feeling in general, but worse for someone high in the power motive (as most published writers are). One way some writers get past that is to start the second book.
Series writers have an advantage here, because you can lay groundwork for the next book. I chuckled when my wife asked me about points of detail in my first book ("how does this vampire get to the store to get bottles of blood if he lives out in the country?") which I had already answered in the second, which is about 20,000 words long. As I mentioned, in this case I worked on the second while I waited for Toni to finish editing the first, but there's no reason why you couldn't pause between drafts, for example. For the record, I deliberately did not choose to explain everything in the first book, or it sounds too much like a "first book." Things I didn't need to explain, I didn't. I wouldn't have been able to do this fifteen years ago -- there are some advantages to age...
When you don't write series, it might be trickier. If you are the kind of writer who likes exploring a certain issue or type of conflict, you could use a second book to help focus the first -- answering the question both ways.
In brief, linearity is overrated!