I'm usually not very good at keeping a journal or diary (see, for example, the regularity with which I write in this particular venue). I've tried several times over the years, because I think that I should, and I never last for very long. At the beginning of the year when so many blogger were posting various stats about their reading habits last year, I decided to keep a log of what I read. "Nothing could be simpler," I thought, "it's just data gathering!"
And so it is. I've got a spreadsheet on google docs. Whenever I start reading a book, I fill in the author and title, whether it's fiction or nonfiction, and the date I started reading. When I finish, I fill in the end date. And I get to do some simple spreadsheet programming to keep various statistics, which is always fun (no, that's not sarcastic, although some people may think it ironic).
There are some operational problems. Whenever I start reading a book, I have to remember to record it, at least within a day or so, so I get the start date right. For some reason, recording the end of a book is easier for me to remember. And, of course, I need to be near a computer; I foresee this causing problems during my summer reading binge, when there's not a computer in sight on the upper reaches of the Ottawa River.
More interesting than these mechanical issues, which are fairly obvious, I've already started to notice some effects on my reading behaviour. I normally read quickly: for my vacation I usually plan to read one book a day (if nothing else, that means I won't run out of books), but so far this year, it's taken an average of six days to finish a book (of those I've completed). The book I just finished yesterday took seventeen days to complete, but that has nothing to do with the difficulty of the book or my lack of interest in it, and everything to do with the fact that I've started a big project, and don't have as much spare time to devote to reading.
Which leads to the biggest effect of keeping a reading journal on my reading habits: I am loathe to start a new book until I know that I'll have time to devote to it. It seems that the incomplete books on my list (two right now, one dating from Christmas), impart a certain weight, and that, for me at least, recording data has moved me from "always have a book on the go" to "promptly finish the books I start." I suspect that I'll read the same number of books regardless, it's just that I won't start them until I have some spare time, so I'll have short reads with large "illiterate" gaps, rather than continuous slow reading.
Of course, if I really wanted to rack up the numbers, I'd just stop reading The Economist every week (but then, I'm falling behind on that too).