I have been tracking my reading since 2004. Originally, I was keeping a hand-witten list of each book as I read it. Then I advanced to using a spreadsheet. In January 2007 I found a site which made it a relatively easy and enjoyable task.
http://www.librarthing.com/ (but more about that later, in detail below)
Why track your reading? Being able to see what you've read is useful in many ways. One can feel a sense of accomplishment when observing what they read, especially if it includes setting goals for your reading. Tracking your reading allows you to give better book recommendations. It allows you to join discussions about books, as well as reading groups. Books are a great way to relate to others. Tracking your reading also allows you to better see the types of books to which you gravitate and might inspire you to stretch yourself to attempt genres you previously ignored.
Using LibraryThing is really very easy. And I'll give you some tips here that will make it even easier. You may use the site to enter up to 200 books for free. Once you determine you wish to enter more than 200 books you may enter as many as you like for $10 a year or simply pay $25 for a lifetime membership to the site. That's what I did, and right away. I also bought a lifetime membership for one of my brothers.
The easiest way to learn about the use and functionality of the site is to follow this tour:
just keep clicking "next" as it goes from tip to tip.
The sit allows users to "tag" or label their books any way they wish. Doing so allows you to sort the books in various ways. Examples of tags include bot are not limited to: fictio, non fiction, mystery, intimacy, juvenile, series, movie tie-ins, month and year read, etc.
Even obscure titles may be added. If the book is not to be found in the 690 libraries associated with the site, you may add it on your own, using the information you have at hand.
The site will display all sorts of facts pertaining directly to the books you log. I find it interesting to look at these every once and a while.
If you join, let me know, and I'll befriend you on the site so we can see each other's bookshelves.