I can't say that I've always been an avid reader. I can say that I've wished that I'd read more in the past and had more time to read now. I collected more books than I ever had time (and, frankly, inclination) to read. And it only got worse when I was transferred to an office that I couldn't commute to by train (my prime reading time).
Anyway, one thing that I noticed was that I really couldn't remember much about a lot of the books that I'd read -- including some characters, parts of the plot, maybe the author's name, even the title! Now some of this might've been the result of poor choices in reading material. That will happen when you get a big chunk of your books from the closeouts and remainders bins. You do save money, but at the cost of better reading material.
So a number of years back, probably around 2000, I started keeping track of the books I was reading, if only so I could refer back to them or to tell a friend about them. A bad thing about reading "leftovers" is that few other people that I know would have read them, so there isn't much to talk about unless I could introduce them to the book.
Later on, someone gave me a great suggestion: create a Notepad file, call it Books03 (it was 2003) and just update it every time I started a new book. Instant record keeping.
The internet allowed me to take it one step further. I have a page on geocities:
Tanniker Smith's Recently Read Books (that's sort of an Internet alias ... long story). The problem is that it's actually a pain to keep up with even though I actually enjoy coding my own pages.
I've been thinking for a while about making a Blogger page out of it. Easier updates. Plus there's an RSS feed in the event that someone might care when I update this page. Obviously, it isn't going to updated too often about what I'm currently reading. Frankly, it still takes me too long to finish things because I just don't have the time.
On the other hand, if I start with my oldest notes from 2000, it will be a while before I catch up to the present day.
EDIT: I discovered a couple of books that I can absolutely remember where I was when I was reading them. And those date to 2001-2002. Given the number of books that I tend to read in a year, that would mean that my little book of notes probably started in 1999 or even 1998.